i18n: localize the editor toolbar in all 23 locales

The rich-text editor was the last hardcoded-English surface in the
composer: 21 tooltip titles, the eight table-menu entries, the "Remove
color" entry and the table size picker's "Pick size" label were plain
strings while every other menu in the app is localized.

All of them now come from a new email_composer.toolbar namespace,
translated into all 23 locales using each platform's established
editor terminology (Word/Docs conventions - de "Formatierung löschen",
ar "مسح التنسيق", ja "書式をクリア", ...). The link prompt stays "URL",
which is the same term in every language.

Tooltips and self-sizing dropdowns have no width constraints, so longer
translations are safe everywhere.

locales/cs/common.json

@@ -686,6 +686,38 @@
     "recipient_name_placeholder": "Zobrazované jméno",
     "autocomplete_search_server": "Hledat na serveru",
     "autocomplete_searching": "Hledání...",
+    "toolbar": {
+      "bold": "Tučné",
+      "italic": "Kurzíva",
+      "underline": "Podtržené",
+      "strikethrough": "Přeškrtnuté",
+      "text_color": "Barva textu",
+      "remove_color": "Odebrat barvu",
+      "heading_1": "Nadpis 1",
+      "heading_2": "Nadpis 2",
+      "bullet_list": "Odrážkový seznam",
+      "ordered_list": "Číslovaný seznam",
+      "quote": "Citace",
+      "code_block": "Blok kódu",
+      "align_left": "Zarovnat vlevo",
+      "align_center": "Na střed",
+      "align_right": "Zarovnat vpravo",
+      "text_direction": "Směr textu (RTL/LTR)",
+      "link": "Odkaz",
+      "table": "Tabulka",
+      "clear_formatting": "Vymazat formátování",
+      "undo": "Zpět",
+      "redo": "Znovu",
+      "add_row_above": "Přidat řádek nad",
+      "add_row_below": "Přidat řádek pod",
+      "add_column_before": "Přidat sloupec před",
+      "add_column_after": "Přidat sloupec za",
+      "delete_row": "Odstranit řádek",
+      "delete_column": "Odstranit sloupec",
+      "toggle_header_row": "Přepnout řádek záhlaví",
+      "delete_table": "Odstranit tabulku",
+      "pick_size": "Vybrat velikost"
+    },
     "send_filing_warning": "Odesláno - ale následný úklid selhal, může zůstat zastaralý koncept."
   },
   "confirm_dialog": {