- Add GET /api/metrics-store/history endpoint for querying SQLite-backed metrics
- Support flexible time ranges: 1h, 6h, 12h, 24h, 7d, 30d, 90d
- Return aggregated data with min/max values for longer time ranges
- Add TypeScript types and ChartsAPI.getMetricsHistory() client method
This enables frontend charts to visualize long-term trends using the
tiered retention system (raw → minute → hourly → daily averages).