fix: drawer open/close updates UI immediately without refresh

- Return null instead of throwing on 404 for drawer current query
- Sync drawer session ID to null when drawer closes
- Await query invalidation before closing dialog
- Fix unused approvedBy lint error

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/backend/src/services/drawer.service.ts

@@ -104,7 +104,7 @@ export const DrawerService = {
     return session ?? null
   },
 
-  async addAdjustment(db: PostgresJsDatabase<any>, sessionId: string, input: DrawerAdjustmentInput, createdBy: string, approvedBy?: string) {
+  async addAdjustment(db: PostgresJsDatabase<any>, sessionId: string, input: DrawerAdjustmentInput, createdBy: string, _approvedBy?: string) {
     const session = await this.getById(db, sessionId)
     if (!session) throw new NotFoundError('Drawer session')
     if (session.status === 'closed') throw new ConflictError('Cannot adjust a closed drawer')