feat(tasks): Add unified task-based worker architecture

Replace fragmented job systems (job_schedules, dispensary_crawl_jobs, SyncOrchestrator)
with a single unified task queue:

- Add worker_tasks table with atomic task claiming via SELECT FOR UPDATE SKIP LOCKED
- Add TaskService for CRUD, claiming, and capacity metrics
- Add TaskWorker with role-based handlers (resync, discovery, analytics)
- Add /api/tasks endpoints for management and migration from legacy systems
- Add TasksDashboard UI and integrate task counts into main dashboard
- Add comprehensive documentation

Task roles: store_discovery, entry_point_discovery, product_discovery, product_resync, analytics_refresh

Run workers with: WORKER_ROLE=product_resync npx tsx src/tasks/task-worker.ts

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

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

backend/src/tasks/handlers/index.ts

@@ -0,0 +1,11 @@
+/**
+ * Task Handlers Index
+ *
+ * Exports all task handlers for the task worker.
+ */
+
+export { handleProductResync } from './product-resync';
+export { handleProductDiscovery } from './product-discovery';
+export { handleStoreDiscovery } from './store-discovery';
+export { handleEntryPointDiscovery } from './entry-point-discovery';
+export { handleAnalyticsRefresh } from './analytics-refresh';