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/lua/src/adapter.dart

@@ -0,0 +1,30 @@
+import 'package:clide/extension/extension.dart';
+
+/// Tier-0 stub. The real adapter wraps a parsed Lua extension manifest
+/// and a handle to the Lua state; contributions are proxied to
+/// callbacks registered by `clide.contribute(...)` from the Lua side.
+class LuaExtension extends ClideExtension {
+  LuaExtension({
+    required this.id,
+    required this.title,
+    required this.version,
+    this.dependsOn = const [],
+  });
+
+  @override
+  final String id;
+  @override
+  final String title;
+  @override
+  final String version;
+  @override
+  final List<String> dependsOn;
+
+  @override
+  List<ContributionPoint> get contributions => const [];
+
+  @override
+  Future<void> activate(ClideExtensionContext ctx) async {
+    throw UnsupportedError('Lua runtime lands at Tier 6.');
+  }
+}