Telemetry catalogue

Core signals include:

• HTTP request rate, duration, and status metrics.
• Puzzle generation duration and fallback gauges.
• Runtime load, rebuild, cache hit, cache miss, and content-pool metrics.
• Traces for daily, historical, current-season, runtime, cache, attempt, share, and health operations.
• Frontend product events such as puzzle_loaded, puzzle_solved, share_clicked, and frontend_error.

When adding a signal, document its name, kind, labels, owner, and operational question. Avoid high-cardinality labels that make a useful metric difficult to aggregate.