feat: add Logs tab with cursor-paginated search, level filters, and live tail
- Extend GET /api/v1/logs with cursor pagination, multi-level filtering,
optional application scoping, and level count aggregation
- Add exchangeId, instanceId, application, mdc fields to log responses
- Refactor ClickHouseLogStore with keyset pagination (N+1 pattern)
- Add LogSearchRequest/LogSearchResponse core domain records
- Create LogSearchPageResponse wrapper DTO
- Add Logs as 4th content tab (Exchanges | Dashboard | Runtime | Logs)
- Implement LogSearch component with debounced search, level filter bar,
expandable log entries, cursor pagination, and live tail mode
- Add cross-navigation: exchange header → logs, log tab → logs tab
- Update ClickHouseLogStoreIT with cursor, multi-level, cross-app tests
Closes: #104
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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