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/widgets/src/icons/folder.dart

@@ -0,0 +1,23 @@
+import 'package:clide/widgets/src/clide_icon.dart';
+import 'package:flutter/widgets.dart';
+
+class FolderIcon extends ClideIconPainter {
+  const FolderIcon();
+
+  @override
+  void paint(Canvas canvas, Color color) {
+    final p = Paint()
+      ..color = color
+      ..style = PaintingStyle.stroke
+      ..strokeWidth = 0.08;
+    final path = Path()
+      ..moveTo(0.08, 0.30)
+      ..lineTo(0.40, 0.30)
+      ..lineTo(0.48, 0.22)
+      ..lineTo(0.92, 0.22)
+      ..lineTo(0.92, 0.80)
+      ..lineTo(0.08, 0.80)
+      ..close();
+    canvas.drawPath(path, p);
+  }
+}