perf: Fix all 7 code analysis issues

HIGH (Performance):
- Replace 8 sync file operations with aiofiles in async context (storage, mail,
  report_generator, dms_bridge, ai_assistant)
- Frontend bundle splitting: manualChunks for react-vendor, ui-components, tanstack,
  markdown, icons, utils, i18n (ui chunk 936K → ~19K)

MEDIUM (Architecture):
- Worker circular deps: Replace direct plugin imports with job_registry.py pattern
  (register_job/get_all_jobs, importlib-based lazy loading)
- App-wide ErrorBoundary: New ErrorBoundary.tsx component, wrapped in AppShell
  and all standalone routes

LOW (Code Quality):
- N+1 query fix: selectinload(Contact.contact_persons) in list_contacts()
- O(n²) dedup fix: SQL GROUP BY for email/phone duplicates, Dict-based name grouping
- Response format standardization: 7 routes converted from plain arrays to
  {items: [...], total: N} format

frontend/src/components/layout/AppShell.tsx

@@ -10,6 +10,7 @@ import { useAIUIControl } from '@/hooks/useAIUIControl';
 import { PluginRegistry } from '@/components/plugins/PluginRegistry';
 import { AIUIControlIndicator } from '@/components/ai-ui-control/AIUIControlIndicator';
 import { WindowContainer } from '@/components/window/WindowContainer';
+import { ErrorBoundary } from '@/components/ErrorBoundary';
 
 export function AppShell() {
   const location = useLocation();
@@ -38,7 +39,9 @@ export function AppShell() {
             id="main-content"
             data-testid="content-area"
           >
-            <Outlet />
+            <ErrorBoundary>
+              <Outlet />
+            </ErrorBoundary>
           </main>
         </div>
       </div>