feat: add Timmy Chat mobile app (Expo/React Native)

- Single-screen chat interface with Timmy's sovereign AI personality
- Text messaging with real-time AI responses via server chat API
- Voice recording and playback with waveform visualization
- Image sharing (camera + photo library) with full-screen viewer
- File attachments via document picker
- Dark arcane theme matching the Timmy Time dashboard
- Custom app icon with glowing T circuit design
- Timmy system prompt ported from dashboard prompts.py
- Unit tests for chat utilities and message types

mobile-app/lib/utils.ts

@@ -0,0 +1,15 @@
+import { clsx, type ClassValue } from "clsx";
+import { twMerge } from "tailwind-merge";
+
+/**
+ * Combines class names using clsx and tailwind-merge.
+ * This ensures Tailwind classes are properly merged without conflicts.
+ *
+ * Usage:
+ * ```tsx
+ * cn("px-4 py-2", isActive && "bg-primary", className)
+ * ```
+ */
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs));
+}