feat: Auto-migrations on startup, worker exit location, proxy improvements

- Add auto-migration system that runs SQL files from migrations/ on server startup
- Track applied migrations in schema_migrations table
- Show proxy exit location in Workers dashboard
- Add "Cleanup Stale" button to remove old workers
- Add remove button for individual workers
- Include proxy location (city, state, country) in worker heartbeats
- Update Proxy interface with location fields
- Re-enable bulk proxy import without ON CONFLICT

🤖 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

@@ -182,12 +182,13 @@ export class TaskWorker {
   }
 
   /**
-   * Send heartbeat to registry with resource usage
+   * Send heartbeat to registry with resource usage and proxy location
    */
   private async sendRegistryHeartbeat(): Promise<void> {
     try {
       const memUsage = process.memoryUsage();
       const cpuUsage = process.cpuUsage();
+      const proxyLocation = this.crawlRotator.getProxyLocation();
 
       await fetch(`${API_BASE_URL}/api/worker-registry/heartbeat`, {
         method: 'POST',
@@ -202,6 +203,7 @@ export class TaskWorker {
             memory_rss_mb: Math.round(memUsage.rss / 1024 / 1024),
             cpu_user_ms: Math.round(cpuUsage.user / 1000),
             cpu_system_ms: Math.round(cpuUsage.system / 1000),
+            proxy_location: proxyLocation,
           }
         })
       });