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>

ui/src/hooks/useScope.ts

@@ -2,9 +2,9 @@
 import { useParams, useNavigate, useLocation } from 'react-router';
 import { useCallback } from 'react';
 
-export type TabKey = 'exchanges' | 'dashboard' | 'runtime';
+export type TabKey = 'exchanges' | 'dashboard' | 'runtime' | 'logs';
 
-const VALID_TABS = new Set<TabKey>(['exchanges', 'dashboard', 'runtime']);
+const VALID_TABS = new Set<TabKey>(['exchanges', 'dashboard', 'runtime', 'logs']);
 
 export interface Scope {
   tab: TabKey;