Add “Game Name” OBS source for active game title

[Copilot]

This PR adds a new source that renders the currently active game title, complementing existing profile/game overlays. The source updates on game-change events and persists its visual configuration like other text sources.

• New source: Game Name

  • Added a new OBS text source (xbox_game_name_source) with display name Game Name.
  • Source text is driven by game_t.title from the active session and clears when no game is active.
  • Uses existing text rendering + auto show/hide infrastructure for consistent behavior.

• Monitoring service surface

  • Added monitoring_get_current_active_game() to expose the current resolved active game.
  • Enables source creation to seed initial text immediately (without waiting for the next event).

• Persistent source configuration

  • Added game_name_configuration_t and state APIs:
    • state_set_game_name_configuration(...)
    • state_get_game_name_configuration()
    • state_free_game_name_configuration(...)
  • Persists font, size, gradient colors, and auto-visibility settings using dedicated state keys.

• Plugin + build integration

  • Registered and cleaned up the new source in module load/unload flow.
  • Added new source file to CMake target sources.
  • Updated README source list to include Game Name under Game sources.

// monitoring_service.h
const game_t *monitoring_get_current_active_game(void);

// game_name.c (source initialization path)
update_game_name(monitoring_get_current_active_game());
monitoring_subscribe_game_played(on_game_played);