Generic Observability Rules for Perplexity Labs

# Generic Observability Rules for Perplexity Labs

## Logging
- Structured JSON logs with level, timestamp, service, requestId.
- No secrets or PII in logs.
- Log business events that matter (checkout completed, subscription canceled).

## Metrics
- Track RED metrics: Rate, Errors, Duration.
- Add domain metrics (MRR events, activation funnel, churn signals).
- Alert on user-impacting symptoms, not raw CPU only.

## Tracing
- Propagate trace IDs across async jobs and service boundaries.
- Add spans around DB calls, external API calls, and queue handlers.