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

apps/web/src/pages/settings/ThemeSettings.tsx

@@ -1,14 +1,10 @@
 import { useState, useEffect, useCallback } from 'react';
 import { Form, Input, Select, Button, ColorPicker, message, Typography } from 'antd';
-import client from '../../api/client';
-
-// --- Types ---
-
-interface ThemeConfig {
-  primary_color?: string;
-  logo_url?: string;
-  sidebar_style?: 'light' | 'dark';
-}
+import {
+  getTheme,
+  updateTheme,
+  type ThemeConfig,
+} from '../../api/themes';
 
 // --- Component ---
 
@@ -20,8 +16,7 @@ export default function ThemeSettings() {
   const fetchTheme = useCallback(async () => {
     setLoading(true);
     try {
-      const { data: resp } = await client.get('/config/themes');
-      const theme: ThemeConfig = resp.data ?? resp;
+      const theme = await getTheme();
       form.setFieldsValue({
         primary_color: theme.primary_color || '#1677ff',
         logo_url: theme.logo_url || '',
@@ -49,7 +44,7 @@ export default function ThemeSettings() {
   }) => {
     setSaving(true);
     try {
-      await client.put('/config/themes', {
+      await updateTheme({
         primary_color:
           typeof values.primary_color === 'string'
             ? values.primary_color