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

app/services/contact_service.py

@@ -175,6 +175,9 @@ async def list_contacts(
     offset = (page - 1) * page_size
     base = base.offset(offset).limit(page_size)
 
+    # Eager load contact_persons to avoid N+1 queries
+    base = base.options(selectinload(Contact.contact_persons))
+
     result = await db.execute(base)
     contacts = result.scalars().all()