Implement critical fixes

Approve and implement Phase 1 critical fixes including CORS, RPC rollback, idempotency, timeouts, and deadlock retry.

src/integrations/supabase/types.ts

@@ -6243,6 +6243,7 @@ export type Database = {
       migrate_user_list_items: { Args: never; Returns: undefined }
       process_approval_transaction: {
         Args: {
+          p_idempotency_key?: string
           p_item_ids: string[]
           p_moderator_id: string
           p_request_id?: string