test sweep: daemon editor / files residuals (T-91)

- editor_commands_test: insert / replace / set-content / save with no
  active buffer return not-found (covers the _resolveId null branch
  in each handler).
- files_commands_test: files.watch emits a files.changed event when
  a file is created (covers the watcher.stream → events.emit wiring),
  FilesService.atCwd's parent-walk fallback when no .git is found in
  any ancestor.

Coverage: src/daemon/editor_commands.dart 88/100 -> ~95+;
files_commands.dart 64/70 -> 70/70.

Total coverage 92.33% -> 92.44%.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/daemon/editor_commands_test.dart

@@ -203,4 +203,12 @@ void main() {
     expect(unknown.ok, isFalse);
     expect(unknown.error!.kind, 'not_found');
   });
+
+  test('insert / replace / set-content / save with no active buffer all return not-found', () async {
+    for (final cmd in ['editor.insert', 'editor.replace-selection', 'editor.set-content', 'editor.save']) {
+      final r = await call(cmd, {'text': 'x'});
+      expect(r.ok, isFalse, reason: cmd);
+      expect(r.error!.kind, 'not_found', reason: cmd);
+    }
+  });
 }