feat(workers): Add proxy reload, staggered tasks, and bulk proxy import

- Periodic proxy reload: Workers now reload proxies every 60s to pick up changes
- Staggered task scheduling: New API endpoints for creating tasks with delays
- Bulk proxy import: Script supports multiple URL formats including host:port:user:pass
- Proxy URL column: Migration 086 adds proxy_url for non-standard formats

Key changes:
- crawl-rotator.ts: Added reloadIfStale(), isStale(), setReloadInterval()
- task-worker.ts: Calls reloadIfStale() in main loop
- task-service.ts: Added createStaggeredTasks() and createAZStoreTasks()
- tasks.ts: Added POST /batch/staggered and /batch/az-stores endpoints
- import-proxies.ts: New script for bulk proxy import
- CLAUDE.md: Documented staggered task workflow

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/tasks/task-worker.ts

@@ -740,6 +740,12 @@ export class TaskWorker {
       this.backoffReason = null;
     }
 
+    // Periodically reload proxies to pick up changes (new proxies, disabled proxies)
+    // This runs every ~60 seconds (controlled by setProxyReloadInterval)
+    if (this.stealthInitialized) {
+      await this.crawlRotator.reloadIfStale();
+    }
+
     // Check for decommission signal
     const shouldDecommission = await this.checkDecommission();
     if (shouldDecommission) {