feat: comprehensive health check with DB, scheduler, cache

- Add /api/v1/health endpoint with component-level checks
- Verify DB connectivity, fail2ban socket, scheduler, session cache
- Add SQLite WAL cleanup on startup (orphan crash files)
- Migration 8: import_log.timestamp → INTEGER UNIX epoch
- Align import_log timestamps with history_archive (already UNIX int)
- Add unit tests for DB cleanup and health router

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/src/types/blocklist.ts

@@ -41,7 +41,7 @@ export interface ImportLogEntry {
   id: number;
   source_id: number | null;
   source_url: string;
-  timestamp: string;
+  timestamp: number;
   ips_imported: number;
   ips_skipped: number;
   errors: string | null;