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/clipboard.dart

@@ -0,0 +1,57 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart' as flutter_services;
+
+/// Typed, per-content-kind clipboard with a plaintext fallback.
+///
+/// Extensions write typed values (`write<GitHunk>(hunk)`) and read in
+/// the same type (`readAs<GitHunk>()`). Anything with a `toPlain`
+/// callback also syncs to the OS clipboard so external apps see
+/// reasonable text. The history ring keeps the last [historyLimit]
+/// entries per type for quick recall.
+class ClideClipboard {
+  ClideClipboard({this.historyLimit = 16});
+
+  final int historyLimit;
+  final Map<Type, List<Object>> _history = {};
+
+  Future<void> write<T extends Object>(
+    T value, {
+    String Function(T)? toPlain,
+  }) async {
+    final bucket = _history.putIfAbsent(T, () => <Object>[]);
+    bucket.insert(0, value);
+    if (bucket.length > historyLimit) bucket.removeLast();
+    if (toPlain != null) {
+      await flutter_services.Clipboard.setData(
+          flutter_services.ClipboardData(text: toPlain(value)));
+    }
+  }
+
+  T? readAs<T extends Object>() {
+    final bucket = _history[T];
+    if (bucket == null || bucket.isEmpty) return null;
+    return bucket.first as T;
+  }
+
+  List<T> historyOf<T extends Object>() {
+    final bucket = _history[T];
+    if (bucket == null) return const [];
+    return bucket.cast<T>().toList(growable: false);
+  }
+
+  Future<String?> readPlain() async {
+    final d = await flutter_services.Clipboard.getData('text/plain');
+    return d?.text;
+  }
+
+  Future<void> writePlain(String text) async {
+    await flutter_services.Clipboard.setData(
+        flutter_services.ClipboardData(text: text));
+    final bucket = _history.putIfAbsent(String, () => <Object>[]);
+    bucket.insert(0, text);
+    if (bucket.length > historyLimit) bucket.removeLast();
+  }
+
+  @visibleForTesting
+  void clear() => _history.clear();
+}