feat: systematic functional audit — fix 18 issues across Phase A/B

Phase A (P1 production blockers):
- A1: Apply IP rate limiting to public routes (login/refresh)
- A2: Publish domain events for workflow instance state transitions
  (completed/suspended/resumed/terminated) via outbox pattern
- A3: Replace hardcoded nil UUID default tenant with dynamic DB lookup
- A4: Add GET /api/v1/audit-logs query endpoint with pagination
- A5: Enhance CORS wildcard warning for production environments

Phase B (P2 functional gaps):
- B1: Remove dead erp-common crate (zero references in codebase)
- B2: Refactor 5 settings pages to use typed API modules instead of
  direct client calls; create api/themes.ts; delete dead errors.ts
- B3: Add resume/suspend buttons to InstanceMonitor page
- B4: Remove unused EventHandler trait from erp-core
- B5: Handle task.completed events in message module (send notifications)
- B6: Wire TimeoutChecker as 60s background task
- B7: Auto-skip ServiceTask nodes instead of crashing the process
- B8: Remove empty register_routes() from ErpModule trait and modules

crates/erp-core/src/events.rs

@@ -31,12 +31,6 @@ impl DomainEvent {
     }
 }
 
-/// 事件处理器 trait
-pub trait EventHandler: Send + Sync {
-    fn event_types(&self) -> Vec<String>;
-    fn handle(&self, event: &DomainEvent) -> impl std::future::Future<Output = anyhow::Result<()>> + Send;
-}
-
 /// 进程内事件总线
 #[derive(Clone)]
 pub struct EventBus {