feat: email a contact or group via the in-app composer

Adds a "Send email to group" action (To / Cc / Bcc) that opens the composer
pre-filled with the group's members in the chosen field, preserving each
member's display name. It is available both in the group context menu (between
"Edit Group" and "Delete") and in the group detail panel's header (shown when
the group has at least one member with an email). The single-contact "Send
email" button in the contact detail panel uses the same path.

Routing is internal, not via mailto:. Contacts is its own route and the composer
lives in the mail route, so the handoff stashes the recipients
(savePendingMailto) and does a client-side router.push("/"); the main route's
existing consumePendingMailto effect opens the composer in the current account.
This avoids the OS mailto handler (which could open a different mail app) and
the protocol round-trip's full-page reload, which dropped the in-memory
per-account JMAP clients of a multi-account session (a logout).

- contacts/page.tsx: openComposeInApp(recipients, field) shared helper;
  handleComposeGroupFromSidebar (deduped "Name <email>" members, empty -> toast)
  and handleComposeContact; wired to the sidebar, group detail, contact detail.
- contact-group-detail.tsx: onComposeGroup(field) prop + To/Cc/Bcc header control
  (shown when the group has emailable members).
- contacts-sidebar.tsx: onComposeGroup(groupId, field) prop + "Send email to
  group" submenu between Edit and Delete.
- contact-detail.tsx: onCompose() prop; the button is no longer a mailto: link.
- mailto.ts: recipient splitter is quote-aware (reuses the composer's
  splitRecipients) so a comma in a display name survives — still useful for real
  OS mailto: links.
- i18n: contacts.groups.send_email{,_to,_cc,_bcc} and no_member_emails across all
  locales.

Display names round-trip via formatRecipient -> parseRecipientList.

app/(main)/[locale]/contacts/page.tsx

@@ -18,7 +18,9 @@ import { ContactImportDialog } from "@/components/contacts/contact-import-dialog
 import { RenameDialog } from "@/components/files/rename-dialog";
 import { exportContacts } from "@/components/contacts/contact-export";
 import { AppTopBannerSlot } from "@/components/plugins/app-top-banner-slot";
-import { useContactStore, getContactDisplayName } from "@/stores/contact-store";
+import { useContactStore, getContactDisplayName, getContactPrimaryEmail } from "@/stores/contact-store";
+import { savePendingMailto } from "@/lib/protocol-handlers/session";
+import { formatRecipient } from "@/lib/email-composer-utils";
 import { useAuthStore, redirectToLogin } from "@/stores/auth-store";
 import { useEmailStore } from "@/stores/email-store";
 import { usePolicyStore } from "@/stores/policy-store";
@@ -461,6 +463,51 @@ export default function ContactsPage() {
     setView("group-edit");
   }, []);
 
+  // Open the in-app composer in the current session rather than routing through
+  // a mailto: URL. `window.location='mailto:'` hands off to the OS handler
+  // (which may open a different mail app), and the mailto protocol round-trip
+  // reloads the app - dropping the in-memory per-account JMAP clients of a
+  // multi-account session, which reads as a logout. Stashing the recipients and
+  // doing a client-side router.push keeps the session and the active account
+  // intact; the main route consumes the pending compose and opens the composer
+  // (see consumePendingMailto in page.tsx).
+  const openComposeInApp = useCallback((recipients: string[], field: "to" | "cc" | "bcc") => {
+    savePendingMailto({
+      to: field === "to" ? recipients : [],
+      cc: field === "cc" ? recipients : [],
+      bcc: field === "bcc" ? recipients : [],
+      subject: "",
+      body: "",
+    });
+    router.push("/");
+  }, [router]);
+
+  const handleComposeGroupFromSidebar = useCallback((groupId: string, field: "to" | "cc" | "bcc") => {
+    // Format each member as "Name <email>" so the composer keeps the display
+    // name (round-trips via formatRecipient -> parseRecipientList). Dedupe by
+    // email, case-insensitively; members without an email are skipped.
+    const seen = new Set<string>();
+    const recipients: string[] = [];
+    for (const member of getGroupMembers(groupId)) {
+      const email = getContactPrimaryEmail(member).trim();
+      const key = email.toLowerCase();
+      if (!email || seen.has(key)) continue;
+      seen.add(key);
+      recipients.push(formatRecipient(getContactDisplayName(member), email));
+    }
+    if (recipients.length === 0) {
+      toast.error(t("groups.no_member_emails"));
+      return;
+    }
+    openComposeInApp(recipients, field);
+  }, [getGroupMembers, t, openComposeInApp]);
+
+  const handleComposeContact = useCallback((contact: ContactCard) => {
+    const email = getContactPrimaryEmail(contact).trim();
+    if (!email) return;
+    openComposeInApp([formatRecipient(getContactDisplayName(contact), email)], "to");
+  }, [openComposeInApp]);
+
   const handleDeleteGroupFromSidebar = useCallback(async (groupId: string) => {
     const confirmed = await confirmDialog({
       title: t("groups.delete_confirm_title"),
@@ -625,6 +672,7 @@ export default function ContactsPage() {
             onEdit={handleEditGroup}
             onDelete={handleDeleteGroup}
             onRemoveMember={handleRemoveGroupMember}
+            onComposeGroup={(field) => handleComposeGroupFromSidebar(selectedGroup.id, field)}
             isMobile={isMobile}
             onSelectMember={(id) => {
               setSelectedContact(id);
@@ -702,6 +750,11 @@ export default function ContactsPage() {
             contact={selectedContact}
             onEdit={handleEdit}
             onDelete={handleDelete}
+            onCompose={
+              selectedContact
+                ? () => handleComposeContact(selectedContact)
+                : undefined
+            }
             onAddToGroup={
               selectedContact
                 ? () => handleAddContactToGroup(selectedContact.id)
@@ -807,6 +860,7 @@ export default function ContactsPage() {
                       onImport={() => setShowImportDialog(true)}
                       onEditGroup={handleEditGroupFromSidebar}
                       onDeleteGroup={handleDeleteGroupFromSidebar}
+                      onComposeGroup={handleComposeGroupFromSidebar}
                       onDropContacts={handleDropContacts}
                       onDropContactsToCategory={handleDropContactsToCategory}
                       onRenameAddressBook={client ? (book) => setRenamingAddressBook(book) : undefined}