refactor(i18n): route remaining extension labels through the catalog (T-468)

Migrate the user-facing strings in menubar, output, search, deeplink, editor,
files, terminal, markdown, and vim to ClideSettings.i18n.string/.interpolated;
extend the existing catalogs and create the missing ones (deeplink, output,
search, markdown, menubar, vim). vim mode labels now resolve through
builtin.vim (default still `-- NORMAL --`, now localizable). A dock-status test
seeds builtin.output so the widget's own i18n lookups resolve instead of
warning into the logRing it counts. No en_US behaviour change (D-21).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/builtin/editor/src/editor_view.dart

@@ -320,9 +320,19 @@ class _EditorViewState extends State<EditorView> {
       builder: (context, _) {
         if (c.buffers.isEmpty) {
           return ClidePaneChrome(
-            title: 'editor',
-            subtitle: 'no buffer · use `clide open <path>` or pick a file in the tree',
-            child: const Center(child: ClideText('Open a file to begin editing.', muted: true)),
+            title: ClideSettings.i18n.string(context, 'chrome.title', namespace: 'builtin.editor', placeholder: 'editor'),
+            subtitle: ClideSettings.i18n.string(
+              context,
+              'subtitle.no-buffer',
+              namespace: 'builtin.editor',
+              placeholder: 'no buffer · use `clide open <path>` or pick a file in the tree',
+            ),
+            child: Center(
+              child: ClideText(
+                ClideSettings.i18n.string(context, 'empty', namespace: 'builtin.editor', placeholder: 'Open a file to begin editing.'),
+                muted: true,
+              ),
+            ),
           );
         }
         return MultitabPane<String>(
@@ -392,7 +402,7 @@ class _TextBody extends StatelessWidget {
       showCursor: true,
     );
     return Semantics(
-      label: 'editor text area',
+      label: ClideSettings.i18n.string(context, 'a11y.text-area', namespace: 'builtin.editor', placeholder: 'editor text area'),
       textField: true,
       multiline: true,
       child: ColoredBox(