Introduce `CalculateTrendFloatWithBaseline` to correctly handle scenarios where previous period metrics (Error Rate, Latency) are zero or missing. This prevents arithmetic errors and distinguishes between "new" data and actual increases ("up") when starting from zero.
Also updates the admin panel dashboard documentation to reflect current project status.
- Add `include_trends` query parameter to enable trend calculation
- Implement trend comparison logic (delta % and direction) against previous periods
- Add support for `last7d`, `last30d`, and `all` time period options
- Update `DashboardSummaryResponse` to include optional `trends` field
- Add helper functions for custom time window aggregation
- Add unit tests for trend calculation and period window logic
- Update feature documentation with new parameters and response schemas
