Observability gaps (metrics + structured logs)

[codihuston]

Cause: Minimal metrics for queue depth, failures, retries, or worker health.
Analysis: Hard to diagnose throughput and failure hot spots.
Acceptance Criteria:

• Metrics for queue depth, task latency, failures, retries, worker availability.
• Structured logs are emitted consistently.
  Solution Approach:
• Add metrics emitter and log structure standardization.