fix: QA — add missing translation namespaces + fix sharedWithMe dead path

- Add 'signatures' translation namespace (27 keys) to locales
- Add 'settings.tabs.signatures' translation key
- Add 'settings.importer' translation namespace (18 keys)
- Fix sharedWithMe never populated in sharing-store — now discovers
  incoming mail/calendar/addressBook shares by checking isShared+myRights

locales/en/common.json

@@ -894,6 +894,7 @@
       "about_data": "About & Data",
       "import": "Import",
       "sharing": "Sharing",
+      "signatures": "Signatures",
       "debug": "Debug"
     },
     "tab_groups": {
@@ -2010,6 +2011,26 @@
       "preview": {
         "label": "Preview"
       }
+    },
+    "importer": {
+      "title": "Import Data",
+      "description": "Import emails from .eml files or .zip/.tgz archives.",
+      "file_label": "Select Files",
+      "file_placeholder": "Choose .eml, .zip, or .tgz files",
+      "folder_label": "Import into Folder",
+      "conflict_label": "If Email Already Exists",
+      "start_import": "Start Import",
+      "importing": "Importing...",
+      "cancel": "Cancel",
+      "success": "Import successful",
+      "fail": "Import failed",
+      "import_complete": "Import Complete",
+      "summary_imported": "{count} imported",
+      "summary_skipped": "{count} skipped",
+      "summary_failed": "{count} failed",
+      "error_details": "Error Details",
+      "import_more": "Import More Files",
+      "progress_title": "Import Progress"
     }
   },
   "errors": {
@@ -3363,5 +3384,45 @@
     "install": "Install",
     "dont_remind": "Don't remind me again",
     "dismiss_aria": "Dismiss install prompt"
+  },
+  "signatures": {
+    "title": "Signatures",
+    "description": "Create and manage email signatures. Assign default signatures for new messages and replies.",
+    "no_signature": "No signatures created yet.",
+    "add_signature": "Add Signature",
+    "duplicate": "Duplicate",
+    "your_signatures": "Your Signatures",
+    "delete_title": "Delete Signature",
+    "delete_message": "Are you sure you want to delete \"{name}\"?",
+    "edit_signature": "Edit Signature",
+    "new_signature": "New Signature",
+    "name_required": "Signature name is required",
+    "name_label": "Signature Name",
+    "name_placeholder": "e.g., Work, Personal, Legal",
+    "editor_label": "Signature Content",
+    "show_preview": "Preview",
+    "show_editor": "Editor",
+    "html_preview_label": "HTML Preview",
+    "plain_text_preview_label": "Plain Text Preview",
+    "default_signature": "Default for new messages",
+    "reply_signature": "Default for replies",
+    "no_signatures_available": "No signatures available",
+    "per_identity_signatures": "Per-Identity Signature Overrides",
+    "per_identity_description": "Assign different signatures to specific identities.",
+    "select_signature": "Select signature",
+    "cancel": "Cancel",
+    "save": "Save Signature",
+    "toolbar": {
+      "bold": "Bold",
+      "italic": "Italic",
+      "underline": "Underline",
+      "strikethrough": "Strikethrough",
+      "link": "Link",
+      "bullet_list": "Bullet List",
+      "ordered_list": "Ordered List",
+      "text_color": "Text Color",
+      "alignment": "Alignment",
+      "font_size": "Font Size"
+    }
   }
 }