fix(tasks): Make pool JOIN defensive when table doesn't exist

Auto-migrate fails early, so task_pools may not exist yet.
Check table existence before including pool columns/joins.

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

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

backend/src/tasks/task-service.ts

@@ -432,7 +432,10 @@ class TaskService {
       params.push(filter.worker_id);
     }
 
-    if (filter.pool_id) {
+    // Check if task_pools table exists for pool filtering
+    const poolsExist = await tableExists('task_pools');
+
+    if (filter.pool_id && poolsExist) {
       conditions.push(`d.pool_id = $${paramIndex++}`);
       params.push(filter.pool_id);
     }
@@ -441,17 +444,20 @@ class TaskService {
     const limit = filter.limit ?? 100;
     const offset = filter.offset ?? 0;
 
+    // Use pool columns only if table exists
+    const poolColumns = poolsExist ? 'd.pool_id as pool_id, tp.display_name as pool_name,' : 'NULL as pool_id, NULL as pool_name,';
+    const poolJoin = poolsExist ? 'LEFT JOIN task_pools tp ON tp.id = d.pool_id' : '';
+
     const result = await pool.query(
       `SELECT
          t.*,
          d.name as dispensary_name,
          d.slug as dispensary_slug,
-         d.pool_id as pool_id,
-         tp.display_name as pool_name,
+         ${poolColumns}
          w.friendly_name as worker_name
        FROM worker_tasks t
        LEFT JOIN dispensaries d ON d.id = t.dispensary_id
-       LEFT JOIN task_pools tp ON tp.id = d.pool_id
+       ${poolJoin}
        LEFT JOIN worker_registry w ON w.worker_id = t.worker_id
        ${whereClause}
        ORDER BY t.created_at DESC