feat: add game event buffering and persistence

This closes #14 (closed)

Introduces a new 'game_events' table and buffering system to track granular game events (inputs, scores, system states) alongside the existing game runs.

Changes:

• db.js:

  • Create game_events table (sensor_id, event_data, timestamp).
  • Add bufferGameEvents function to handle JSON event serialization.
  • Update flushBuffer to perform a single transaction for both runs and events.
  • Wrap database initialization in a transaction for safety.

• server.js:

  • Integrate bufferGameEvents into sendMonitorEvent for automatic logging.
  • Add source tracking (arduino vs frontend) to input events.
  • Add system events for client/monitor connections and disconnections.
  • Capture 'speed' events from Arduino.