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

CMakeLists.txt

@@ -25,6 +25,8 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 # Homebrew: brew install sdl3
 find_package(SDL3 CONFIG REQUIRED)
 find_package(SDL3_ttf CONFIG REQUIRED)
+find_package(cpr CONFIG REQUIRED)
+find_package(nlohmann_json CONFIG REQUIRED)
 
 add_executable(tetris
     src/main.cpp
@@ -82,7 +84,7 @@ if (WIN32)
     )
 endif()
 
-target_link_libraries(tetris PRIVATE SDL3::SDL3 SDL3_ttf::SDL3_ttf)
+target_link_libraries(tetris PRIVATE SDL3::SDL3 SDL3_ttf::SDL3_ttf cpr::cpr nlohmann_json::nlohmann_json)
 
 if (WIN32)
     target_link_libraries(tetris PRIVATE mfplat mfreadwrite mfuuid)
@@ -156,7 +158,7 @@ if (WIN32)
     )
 endif()
 
-target_link_libraries(tetris_refactored PRIVATE SDL3::SDL3 SDL3_ttf::SDL3_ttf)
+target_link_libraries(tetris_refactored PRIVATE SDL3::SDL3 SDL3_ttf::SDL3_ttf cpr::cpr nlohmann_json::nlohmann_json)
 
 if (WIN32)
     target_link_libraries(tetris_refactored PRIVATE mfplat mfreadwrite mfuuid)