wire builtin.editor to the active buffer + open files from the tree

EditorController mirrors the daemon's active buffer into the Flutter
UI. Hydrates on mount (editor.active → editor.read), subscribes to
editor.opened / active-changed / edited / saved / closed, and pushes
local edits back via editor.set-content. A one-shot echo-suppression
flag keeps the daemon's authoritative edit echo from clobbering the
caret the user just moved.

Text surface is EditableText directly — no TextField / Material
import, so D-007's "bare WidgetsApp" guardrail carries into the
editor tab. JetBrainsMono via the shared mono-family constants;
cursor + selection colours come from the theme tokens.

File-tree click now calls ipc.request('editor.open', {path}) instead
of the kernel command registry (which wouldn't have reached the
daemon). The opened file becomes active, the editor tab's controller
sees editor.active-changed, and the text content reconciles.

Linux release bundle still builds; 174 app tests + 74 core tests
stay green.

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

app/lib/builtin/files/src/file_tree_view.dart

@@ -197,11 +197,14 @@ class _FileRow extends StatelessWidget {
 
   void _openFile(BuildContext context, String path) {
     final kernel = ClideKernel.of(context);
-    // editor.open is a Tier-2 command; the registry's contract takes
-    // a positional argv, so pass the path as argv[0]. Response is
-    // ignored — until the editor extension registers the handler,
-    // execute() returns a not-found error.
-    unawaited(kernel.commands.execute('editor.open', args: [path]));
+    // editor.open is a daemon-side IPC handler (lib/src/daemon/
+    // editor_commands.dart), not a kernel command. Fire the request
+    // and let the editor extension's controller pick up the
+    // editor.active-changed / editor.opened event — no need to await
+    // or handle the response here.
+    unawaited(
+      kernel.ipc.request('editor.open', args: {'path': path}),
+    );
   }
 }