feat(scheduler): Immutable schedules and HTTP-only pipeline

## Changes
- **Migration 089**: Add is_immutable and method columns to task_schedules
  - Per-state product_discovery schedules (4h default)
  - Store discovery weekly (168h)
  - All schedules use HTTP transport (Puppeteer/browser)
- **Task Scheduler**: HTTP-only product discovery with per-state scheduling
  - Each state has its own immutable schedule
  - Schedules can be edited (interval/priority) but not deleted
- **TasksDashboard UI**: Full immutability support
  - Lock icon for immutable schedules
  - State and Method columns in schedules table
  - Disabled delete for immutable, restricted edit fields
- **Store Discovery HTTP**: Auto-queue product_discovery for new stores
- **Migration 088**: Discovery payloads storage schema

🤖 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

@@ -75,6 +75,7 @@ import { handleProductRefresh } from './handlers/product-refresh';
 import { handleProductDiscovery } from './handlers/product-discovery-curl';
 import { handleProductDiscoveryHttp } from './handlers/product-discovery-http';
 import { handleStoreDiscovery } from './handlers/store-discovery';
+import { handleStoreDiscoveryHttp } from './handlers/store-discovery-http';
 import { handleEntryPointDiscovery } from './handlers/entry-point-discovery';
 import { handleAnalyticsRefresh } from './handlers/analytics-refresh';
 import { handleWhoami } from './handlers/whoami';
@@ -160,21 +161,30 @@ const TASK_HANDLERS: Record<TaskRole, TaskHandler> = {
 /**
  * Get the appropriate handler for a task, considering both role and method.
  *
- * For product_discovery:
- * - method='http' -> handleProductDiscoveryHttp (browser-based, for Evomi proxies)
- * - method='curl' or unspecified -> handleProductDiscovery (curl-based)
+ * Dual-transport handlers:
+ * - product_discovery: curl (axios) or http (Puppeteer)
+ * - store_discovery: curl (axios) or http (Puppeteer)
+ *
+ * Default method is 'http' since all GraphQL queries should use browser transport
+ * for better TLS fingerprinting and session-based proxy compatibility.
  */
 function getHandlerForTask(task: WorkerTask): TaskHandler | undefined {
   const role = task.role as TaskRole;
-  const method = task.method || 'curl';
+  const method = task.method || 'http'; // Default to HTTP for all GraphQL tasks
 
-  // Special handling for product_discovery with method='http'
+  // product_discovery: dual-transport support
   if (role === 'product_discovery' && method === 'http') {
     console.log(`[TaskWorker] Using HTTP handler for product_discovery (method=${method})`);
     return handleProductDiscoveryHttp;
   }
 
-  // Default: use the static handler registry
+  // store_discovery: dual-transport support
+  if (role === 'store_discovery' && method === 'http') {
+    console.log(`[TaskWorker] Using HTTP handler for store_discovery (method=${method})`);
+    return handleStoreDiscoveryHttp;
+  }
+
+  // Default: use the static handler registry (curl-based)
   return TASK_HANDLERS[role];
 }
 
@@ -719,6 +729,20 @@ export class TaskWorker {
     // Start registry heartbeat immediately
     this.startRegistryHeartbeat();
 
+    // Cleanup stale tasks on startup (only worker-0 does this to avoid races)
+    // This handles tasks left in 'claimed'/'running' status when workers restart
+    if (this.workerId.endsWith('-0') || this.workerId === 'scraper-worker-0') {
+      try {
+        console.log(`[TaskWorker] ${this.friendlyName} running stale task cleanup...`);
+        const cleanupResult = await taskService.cleanupStaleTasks(30); // 30 minute threshold
+        if (cleanupResult.cleaned > 0) {
+          console.log(`[TaskWorker] Cleaned up ${cleanupResult.cleaned} stale tasks`);
+        }
+      } catch (err: any) {
+        console.error(`[TaskWorker] Stale task cleanup error:`, err.message);
+      }
+    }
+
     const roleMsg = this.role ? `for role: ${this.role}` : '(role-agnostic - any task)';
     console.log(`[TaskWorker] ${this.friendlyName} starting ${roleMsg} (stealth=lazy, max ${this.maxConcurrentTasks} concurrent tasks)`);