dissolve app/ into repo root (D-056)

Single Flutter package at the repo root. All code, tests, assets,
and platform directories moved from app/ to root. Package renamed
from clide_app to clide — all imports rewritten. Merged pubspec
combines core (ffi) and app (flutter, yaml, xterm) dependencies.
Makefile simplified: no APP_PRESENT conditionals, no cd, no daemon
lifecycle. 317 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/kernel/src/commands/registry.dart

@@ -0,0 +1,37 @@
+import 'package:clide/clide.dart';
+import 'package:clide/extension/src/contribution.dart';
+import 'package:flutter/foundation.dart';
+
+class CommandRegistry extends ChangeNotifier {
+  final Map<String, CommandContribution> _byCommand = {};
+
+  void register(CommandContribution cmd) {
+    _byCommand[cmd.command] = cmd;
+    notifyListeners();
+  }
+
+  void unregister(String command) {
+    if (_byCommand.remove(command) != null) notifyListeners();
+  }
+
+  Iterable<CommandContribution> get all => _byCommand.values;
+  CommandContribution? get(String command) => _byCommand[command];
+
+  Future<IpcResponse> execute(
+    String command, {
+    List<String> args = const [],
+  }) async {
+    final c = _byCommand[command];
+    if (c == null) {
+      return IpcResponse.err(
+        id: '',
+        error: IpcError(
+          code: IpcExitCode.notFound,
+          kind: IpcErrorKind.notFound,
+          message: 'no such command: $command',
+        ),
+      );
+    }
+    return c.run(args);
+  }
+}