fix(message): resolve Phase 5-6 audit findings

- Add missing version column to all message tables (migration + entities)
- Replace N+1 mark_all_read loop with single batch UPDATE query
- Fix NotificationList infinite re-render (extract queryFilter to stable ref)
- Fix NotificationPreferences dynamic import and remove unused Dayjs type
- Add Semaphore (max 8) to event listener for backpressure control
- Add /docs/openapi.json endpoint for API documentation
- Add permission check to unread_count handler
- Add version: Set(1) to all ActiveModel inserts

crates/erp-server/src/handlers/mod.rs

@@ -1 +1,2 @@
 pub mod health;
+pub mod openapi;