Feature: recipient autocomplete from Sent, with on-demand server search

Compose recipient fields only suggested existing contacts and directory
users, so people you had emailed before but never saved as a contact
never came up. This adds an Outlook-Web-style suggestion flow.

On startup the Sent folder is read once (metadata only) to build a cache
of addresses you have written to; those are merged into the autocomplete
after contacts and directory principals, deduped, contacts winning.

When the recipient is not in the cache, the dropdown offers a "search the
server" row that queries the Sent folder on demand. That lookup fetches
only the to/cc fields (no subject, body or attachments) and returns the
matching addresses, deduped.

New strings are added to all 20 locales.

locales/cs/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Upravit e-mailovou adresu",
     "recipient_edit_name": "Upravit zobrazované jméno",
     "recipient_email_placeholder": "E-mailová adresa",
-    "recipient_name_placeholder": "Zobrazované jméno"
+    "recipient_name_placeholder": "Zobrazované jméno",
+    "autocomplete_search_server": "Hledat na serveru",
+    "autocomplete_searching": "Hledání..."
   },
   "confirm_dialog": {
     "confirm": "Potvrdit",

locales/da/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Rediger e-mailadresse",
     "recipient_edit_name": "Rediger visningsnavn",
     "recipient_email_placeholder": "E-mailadresse",
-    "recipient_name_placeholder": "Visningsnavn"
+    "recipient_name_placeholder": "Visningsnavn",
+    "autocomplete_search_server": "Søg på serveren",
+    "autocomplete_searching": "Søger..."
   },
   "confirm_dialog": {
     "confirm": "Bekræft",

locales/de/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "E-Mail-Adresse bearbeiten",
     "recipient_edit_name": "Anzeigenamen bearbeiten",
     "recipient_email_placeholder": "E-Mail-Adresse",
-    "recipient_name_placeholder": "Anzeigename"
+    "recipient_name_placeholder": "Anzeigename",
+    "autocomplete_search_server": "Auf dem Server suchen",
+    "autocomplete_searching": "Suche läuft..."
   },
   "confirm_dialog": {
     "confirm": "Bestätigen",

locales/en/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Edit email address",
     "recipient_edit_name": "Edit display name",
     "recipient_email_placeholder": "Email address",
-    "recipient_name_placeholder": "Display name"
+    "recipient_name_placeholder": "Display name",
+    "autocomplete_search_server": "Search the server",
+    "autocomplete_searching": "Searching..."
   },
   "confirm_dialog": {
     "confirm": "Confirm",

locales/es/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Editar dirección de correo",
     "recipient_edit_name": "Editar nombre para mostrar",
     "recipient_email_placeholder": "Dirección de correo",
-    "recipient_name_placeholder": "Nombre para mostrar"
+    "recipient_name_placeholder": "Nombre para mostrar",
+    "autocomplete_search_server": "Buscar en el servidor",
+    "autocomplete_searching": "Buscando..."
   },
   "confirm_dialog": {
     "confirm": "Confirmar",

locales/fa/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "ویرایش آدرس ایمیل",
     "recipient_edit_name": "ویرایش نام نمایشی",
     "recipient_email_placeholder": "آدرس ایمیل",
-    "recipient_name_placeholder": "نام نمایشی"
+    "recipient_name_placeholder": "نام نمایشی",
+    "autocomplete_search_server": "جستجو در سرور",
+    "autocomplete_searching": "در حال جستجو..."
   },
   "confirm_dialog": {
     "confirm": "تأیید",

locales/fr/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Modifier l'adresse e-mail",
     "recipient_edit_name": "Modifier le nom d'affichage",
     "recipient_email_placeholder": "Adresse e-mail",
-    "recipient_name_placeholder": "Nom d'affichage"
+    "recipient_name_placeholder": "Nom d'affichage",
+    "autocomplete_search_server": "Rechercher sur le serveur",
+    "autocomplete_searching": "Recherche en cours..."
   },
   "confirm_dialog": {
     "confirm": "Confirmer",

locales/hu/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "E-mail-cím szerkesztése",
     "recipient_edit_name": "Megjelenített név szerkesztése",
     "recipient_email_placeholder": "E-mail-cím",
-    "recipient_name_placeholder": "Megjelenített név"
+    "recipient_name_placeholder": "Megjelenített név",
+    "autocomplete_search_server": "Keresés a kiszolgálón",
+    "autocomplete_searching": "Keresés..."
   },
   "confirm_dialog": {
     "confirm": "Megerősítés",

locales/it/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Modifica indirizzo email",
     "recipient_edit_name": "Modifica nome visualizzato",
     "recipient_email_placeholder": "Indirizzo email",
-    "recipient_name_placeholder": "Nome visualizzato"
+    "recipient_name_placeholder": "Nome visualizzato",
+    "autocomplete_search_server": "Cerca nel server",
+    "autocomplete_searching": "Ricerca in corso..."
   },
   "confirm_dialog": {
     "confirm": "Conferma",

locales/ja/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "メールアドレスを編集",
     "recipient_edit_name": "表示名を編集",
     "recipient_email_placeholder": "メールアドレス",
-    "recipient_name_placeholder": "表示名"
+    "recipient_name_placeholder": "表示名",
+    "autocomplete_search_server": "サーバーを検索",
+    "autocomplete_searching": "検索中..."
   },
   "confirm_dialog": {
     "confirm": "確認",

locales/ko/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "이메일 주소 편집",
     "recipient_edit_name": "표시 이름 편집",
     "recipient_email_placeholder": "이메일 주소",
-    "recipient_name_placeholder": "표시 이름"
+    "recipient_name_placeholder": "표시 이름",
+    "autocomplete_search_server": "서버에서 검색",
+    "autocomplete_searching": "검색 중..."
   },
   "confirm_dialog": {
     "confirm": "확인",

locales/lv/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Rediģēt e-pasta adresi",
     "recipient_edit_name": "Rediģēt parādāmo vārdu",
     "recipient_email_placeholder": "E-pasta adrese",
-    "recipient_name_placeholder": "Parādāmais vārds"
+    "recipient_name_placeholder": "Parādāmais vārds",
+    "autocomplete_search_server": "Meklēt serverī",
+    "autocomplete_searching": "Meklē..."
   },
   "confirm_dialog": {
     "confirm": "Apstiprināt",

locales/nl/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "E-mailadres bewerken",
     "recipient_edit_name": "Weergavenaam bewerken",
     "recipient_email_placeholder": "E-mailadres",
-    "recipient_name_placeholder": "Weergavenaam"
+    "recipient_name_placeholder": "Weergavenaam",
+    "autocomplete_search_server": "Op de server zoeken",
+    "autocomplete_searching": "Bezig met zoeken..."
   },
   "confirm_dialog": {
     "confirm": "Bevestigen",

locales/pl/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Edytuj adres e-mail",
     "recipient_edit_name": "Edytuj wyświetlaną nazwę",
     "recipient_email_placeholder": "Adres e-mail",
-    "recipient_name_placeholder": "Wyświetlana nazwa"
+    "recipient_name_placeholder": "Wyświetlana nazwa",
+    "autocomplete_search_server": "Szukaj na serwerze",
+    "autocomplete_searching": "Wyszukiwanie..."
   },
   "confirm_dialog": {
     "confirm": "Potwierdź",

locales/pt/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Editar endereço de e-mail",
     "recipient_edit_name": "Editar nome de exibição",
     "recipient_email_placeholder": "Endereço de e-mail",
-    "recipient_name_placeholder": "Nome de exibição"
+    "recipient_name_placeholder": "Nome de exibição",
+    "autocomplete_search_server": "Pesquisar no servidor",
+    "autocomplete_searching": "Pesquisando..."
   },
   "confirm_dialog": {
     "confirm": "Confirmar",

locales/ro/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Editați adresa de e-mail",
     "recipient_edit_name": "Editați numele afișat",
     "recipient_email_placeholder": "Adresă de e-mail",
-    "recipient_name_placeholder": "Numele afișat"
+    "recipient_name_placeholder": "Numele afișat",
+    "autocomplete_search_server": "Caută pe server",
+    "autocomplete_searching": "Se caută..."
   },
   "confirm_dialog": {
     "confirm": "Confirmare",

locales/ru/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Изменить адрес эл. почты",
     "recipient_edit_name": "Изменить отображаемое имя",
     "recipient_email_placeholder": "Адрес эл. почты",
-    "recipient_name_placeholder": "Отображаемое имя"
+    "recipient_name_placeholder": "Отображаемое имя",
+    "autocomplete_search_server": "Искать на сервере",
+    "autocomplete_searching": "Поиск..."
   },
   "confirm_dialog": {
     "confirm": "Подтвердить",

locales/tr/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "E-posta adresini düzenle",
     "recipient_edit_name": "Görünen adı düzenle",
     "recipient_email_placeholder": "E-posta adresi",
-    "recipient_name_placeholder": "Görünen ad"
+    "recipient_name_placeholder": "Görünen ad",
+    "autocomplete_search_server": "Sunucuda ara",
+    "autocomplete_searching": "Aranıyor..."
   },
   "confirm_dialog": {
     "confirm": "Onayla",

locales/uk/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "Змінити адресу ел. пошти",
     "recipient_edit_name": "Змінити відображуване ім'я",
     "recipient_email_placeholder": "Адреса ел. пошти",
-    "recipient_name_placeholder": "Відображуване ім'я"
+    "recipient_name_placeholder": "Відображуване ім'я",
+    "autocomplete_search_server": "Шукати на сервері",
+    "autocomplete_searching": "Пошук..."
   },
   "confirm_dialog": {
     "confirm": "Підтвердити",

locales/zh/common.json

@@ -677,7 +677,9 @@
     "recipient_edit_email": "编辑电子邮件地址",
     "recipient_edit_name": "编辑显示名称",
     "recipient_email_placeholder": "电子邮件地址",
-    "recipient_name_placeholder": "显示名称"
+    "recipient_name_placeholder": "显示名称",
+    "autocomplete_search_server": "在服务器上搜索",
+    "autocomplete_searching": "搜索中..."
   },
   "confirm_dialog": {
     "confirm": "确认",