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/clide_surface.dart

@@ -0,0 +1,42 @@
+import 'package:clide/kernel/src/theme/controller.dart';
+import 'package:flutter/widgets.dart';
+
+/// Themed container. Replaces Material's Card / Scaffold body surfaces
+/// for clide widgets — pulls color, border, and padding from the
+/// current theme's surface tokens.
+class ClideSurface extends StatelessWidget {
+  const ClideSurface({
+    super.key,
+    this.child,
+    this.color,
+    this.border,
+    this.padding = EdgeInsets.zero,
+    this.width,
+    this.height,
+    this.borderRadius,
+  });
+
+  final Widget? child;
+  final Color? color;
+  final Color? border;
+  final EdgeInsetsGeometry padding;
+  final double? width;
+  final double? height;
+  final BorderRadius? borderRadius;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = ClideTheme.of(context).surface;
+    return Container(
+      width: width,
+      height: height,
+      padding: padding,
+      decoration: BoxDecoration(
+        color: color ?? tokens.panelBackground,
+        border: border == null ? null : Border.all(color: border!, width: 1),
+        borderRadius: borderRadius,
+      ),
+      child: child,
+    );
+  }
+}