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/es/common.json

@@ -686,6 +686,38 @@
     "recipient_name_placeholder": "Nombre para mostrar",
     "autocomplete_search_server": "Buscar en el servidor",
     "autocomplete_searching": "Buscando...",
+    "toolbar": {
+      "bold": "Negrita",
+      "italic": "Cursiva",
+      "underline": "Subrayado",
+      "strikethrough": "Tachado",
+      "text_color": "Color del texto",
+      "remove_color": "Quitar color",
+      "heading_1": "Encabezado 1",
+      "heading_2": "Encabezado 2",
+      "bullet_list": "Lista con viñetas",
+      "ordered_list": "Lista numerada",
+      "quote": "Cita",
+      "code_block": "Bloque de código",
+      "align_left": "Alinear a la izquierda",
+      "align_center": "Centrar",
+      "align_right": "Alinear a la derecha",
+      "text_direction": "Dirección del texto (RTL/LTR)",
+      "link": "Enlace",
+      "table": "Tabla",
+      "clear_formatting": "Borrar formato",
+      "undo": "Deshacer",
+      "redo": "Rehacer",
+      "add_row_above": "Añadir fila encima",
+      "add_row_below": "Añadir fila debajo",
+      "add_column_before": "Añadir columna antes",
+      "add_column_after": "Añadir columna después",
+      "delete_row": "Eliminar fila",
+      "delete_column": "Eliminar columna",
+      "toggle_header_row": "Alternar fila de encabezado",
+      "delete_table": "Eliminar tabla",
+      "pick_size": "Elegir tamaño"
+    },
     "send_filing_warning": "Enviado - pero la limpieza posterior falló, puede quedar un borrador obsoleto."
   },
   "confirm_dialog": {