open markdown files in the reader, not the editor

The files panel and the Claude Config tab called ipc.request('editor.open')
for every file, which targets the editor — so a .md click never reached the
right-side markdown reader (it opens only when something publishes
('builtin.markdown','selection')). Route .md clicks from the files panel
(tree + filtered rows), the Config tab's file-backed rows, and .md wiki links
in the viewer to that channel; non-.md files still open in the editor. Also
remove the dead DaemonEvent fallback that listened for 'editor.buffer_activated'
(the registry emits 'editor.active-changed').

T-187.

Co-Authored-By: Claude <noreply@anthropic.com>

lib/builtin/claude/src/claude_meta_sidebar.dart

@@ -535,7 +535,8 @@ class _ClaudeMetaSidebarState extends State<ClaudeMetaSidebar> {
   }
 
   /// A tappable row for file-backed items (skills, agents, commands).
-  /// Fires `editor.open` with the path when tapped (D-6, T-183).
+  /// All config items are .md files — opens in the markdown reader panel
+  /// via the kernel MessageBus (D-6, T-183).
   Widget _configFileRow(SurfaceTokens tokens, String name, String? path) {
     final row = Padding(
       padding: const EdgeInsets.only(left: 16, top: 2, bottom: 2),
@@ -546,14 +547,15 @@ class _ClaudeMetaSidebarState extends State<ClaudeMetaSidebar> {
       ),
     );
     if (path == null) return row;
+    void openMarkdown() => ClideKernel.of(context).messages.publish('builtin.markdown', 'selection', {'path': path});
     return Semantics(
       button: true,
       label: name,
       excludeSemantics: true,
-      onTap: () => unawaited(ClideKernel.of(context).ipc.request('editor.open', args: {'path': path})),
+      onTap: openMarkdown,
       child: ClideTappable(
         tooltip: path,
-        onTap: () => unawaited(ClideKernel.of(context).ipc.request('editor.open', args: {'path': path})),
+        onTap: openMarkdown,
         builder: (ctx, hovered, _) => Padding(
           padding: const EdgeInsets.only(left: 16, top: 2, bottom: 2),
           child: ClideText(