feat: Add Firebase high score sync, menu music, and gameplay improvements

- Integrate Firebase Realtime Database for high score synchronization
  - Add cpr and nlohmann-json dependencies for HTTP requests
  - Implement async score loading from Firebase with local fallback
  - Submit all scores > 0 to Firebase in background thread
  - Always prompt for player name on game over if score > 0

- Add dedicated menu music system
  - Implement menu track support in Audio class with looping
  - Add "Every Block You Take.mp3" as main menu theme
  - Automatically switch between menu and game music on state transitions
  - Load menu track asynchronously to prevent startup delays

- Update level speed progression to match web version
  - Replace NES frame-based gravity with explicit millisecond values
  - Implement 20-level speed table (1000ms to 60ms)
  - Ensure consistent gameplay between C++ and web versions

- Fix startup performance issues
  - Move score loading to background thread to prevent UI freeze
  - Optimize Firebase network requests with 2s timeout
  - Add graceful fallback to local scores on network failure

Files modified:
- src/persistence/Scores.cpp/h - Firebase integration
- src/audio/Audio.cpp/h - Menu music support
- src/core/GravityManager.cpp/h - Level speed updates
- src/main.cpp - State-based music switching, async loading
- CMakeLists.txt - Add cpr and nlohmann-json dependencies
- vcpkg.json - Update dependency list

src/core/GravityManager.cpp

@@ -14,19 +14,19 @@ double GravityManager::getGlobalMultiplier() const { return globalMultiplier; }
 
 void GravityManager::setLevelMultiplier(int level, double m) {
     if (level < 0) return;
-    int idx = level >= 29 ? 29 : level;
+    int idx = level >= 19 ? 19 : level;
     levelMultipliers[idx] = std::clamp(m, 0.01, 100.0);
 }
 
 double GravityManager::getLevelMultiplier(int level) const {
-    int idx = level < 0 ? 0 : (level >= 29 ? 29 : level);
+    int idx = level < 0 ? 0 : (level >= 19 ? 19 : level);
     return levelMultipliers[idx];
 }
 
 double GravityManager::getMsForLevel(int level) const {
-    int idx = level < 0 ? 0 : (level >= 29 ? 29 : level);
-    double frames = static_cast<double>(FRAMES_TABLE[idx]) * levelMultipliers[idx];
-    double result = frames * FRAME_MS * globalMultiplier;
+    int idx = level < 0 ? 0 : (level >= 19 ? 19 : level);
+    double baseMs = LEVEL_SPEEDS_MS[idx];
+    double result = baseMs * levelMultipliers[idx] * globalMultiplier;
     return std::max(1.0, result);
 }