feat: Parallelized store discovery, modification tracking, and task deduplication

Store Discovery Parallelization:
- Add store_discovery_state handler for per-state parallel discovery
- Add POST /api/tasks/batch/store-discovery endpoint
- 8 workers can now process states in parallel (~30-45 min vs 3+ hours)

Modification Tracking (Migration 090):
- Add last_modified_at, last_modified_by_task, last_modified_task_id to dispensaries
- Add same columns to store_products
- Update all handlers to set tracking info on modifications

Stale Task Recovery:
- Add periodic stale cleanup every 10 minutes (worker-0 only)
- Prevents orphaned tasks from blocking queue after worker crashes

Task Deduplication:
- createStaggeredTasks now skips if pending/active task exists for same role
- Skips if same role completed within last 4 hours
- API responses include skipped count

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

backend/src/discovery/promotion.ts

@@ -131,6 +131,14 @@ export interface PromotionSummary {
   newDispensaryIds: number[];
 }
 
+/**
+ * Task tracking info for modification audit trail
+ */
+export interface TaskTrackingInfo {
+  taskId: number;
+  taskRole: string;
+}
+
 /**
  * Generate a URL-safe slug from name and city
  */
@@ -283,7 +291,8 @@ async function ensureCrawlerProfile(
  * Idempotent: uses ON CONFLICT on platform_dispensary_id
  */
 async function promoteLocation(
-  loc: DiscoveryLocationRow
+  loc: DiscoveryLocationRow,
+  taskTracking?: TaskTrackingInfo
 ): Promise<PromotionResult> {
   const slug = loc.platform_slug || generateSlug(loc.name, loc.city || '', loc.state_code || '');
 
@@ -325,13 +334,16 @@ async function promoteLocation(
       dutchie_verified,
       dutchie_verified_at,
       dutchie_discovery_id,
+      last_modified_at,
+      last_modified_by_task,
+      last_modified_task_id,
       created_at,
       updated_at
     ) VALUES (
       $1, $2, $3, $4, $5, $6, $7, $8, $9, $10,
       $11, $12, $13, $14, $15, $16, $17, $18, $19, $20,
       $21, $22, $23, $24, $25, $26, $27, $28, $29, $30,
-      $31, $32, $33, $34, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP
+      $31, $32, $33, $34, $35, $36, $37, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP
     )
     ON CONFLICT (platform_dispensary_id) WHERE platform_dispensary_id IS NOT NULL
     DO UPDATE SET
@@ -362,6 +374,9 @@ async function promoteLocation(
       country = EXCLUDED.country,
       status = EXCLUDED.status,
       dutchie_discovery_id = EXCLUDED.dutchie_discovery_id,
+      last_modified_at = EXCLUDED.last_modified_at,
+      last_modified_by_task = EXCLUDED.last_modified_by_task,
+      last_modified_task_id = EXCLUDED.last_modified_task_id,
       updated_at = CURRENT_TIMESTAMP
     RETURNING id, (xmax = 0) AS inserted
   `, [
@@ -399,6 +414,9 @@ async function promoteLocation(
     true,                                          // $32 dutchie_verified
     new Date(),                                    // $33 dutchie_verified_at
     loc.id,                                        // $34 dutchie_discovery_id
+    taskTracking ? new Date() : null,              // $35 last_modified_at
+    taskTracking?.taskRole || null,                // $36 last_modified_by_task
+    taskTracking?.taskId || null,                  // $37 last_modified_task_id
   ]);
 
   const dispensaryId = upsertResult.rows[0].id;
@@ -446,10 +464,12 @@ async function promoteLocation(
  *
  * @param stateCode Optional filter by state (e.g., 'CA', 'AZ')
  * @param dryRun If true, only validate without making changes
+ * @param taskTracking Optional task info for modification audit trail
  */
 export async function promoteDiscoveredLocations(
   stateCode?: string,
-  dryRun = false
+  dryRun = false,
+  taskTracking?: TaskTrackingInfo
 ): Promise<PromotionSummary> {
   const startTime = Date.now();
 
@@ -524,7 +544,7 @@ export async function promoteDiscoveredLocations(
     }
 
     try {
-      const promotionResult = await promoteLocation(loc);
+      const promotionResult = await promoteLocation(loc, taskTracking);
       results.push(promotionResult);
 
       if (promotionResult.action === 'created') {