feat(step-3.6): cloud provider integrations (Gmail, Outlook, Teams)

- Add app/integrations/__init__.py: Fernet token encryption helpers,
  EmailMessage/ChatMessage dataclasses, get_provider() factory
- Add app/integrations/gmail.py: GmailClient with async fetch_messages(),
  token refresh, configurable label/sender/date filters
- Add app/integrations/ms_graph.py: MSGraphClient with fetch_emails()
  (Outlook) and fetch_messages() (Teams), MSAL token refresh, OData filters
- Update app/core/agent_runner.py: replace run_cloud_agent() stub with
  full 8-step implementation; extend _finalize_run() for cloud config type
- Update app/config/settings.py: add OAuth + Fernet encryption settings
- Update requirements.txt: google-api-python-client, google-auth-*,
  msal, cryptography
- Add tests/test_integrations.py: 47 tests covering all integration code
- Update tests/test_agent_runner.py: replace stub test with 7 real tests

All 76 new/updated tests pass.

docker-compose.yml

@@ -8,6 +8,9 @@ services:
         required: false
     environment:
       DATABASE_URL: postgresql+asyncpg://postgres:postgres@db:5432/adiuva
+      GITHUB_COPILOT_TOKEN_DIR: /root/.config/litellm/github_copilot
+    volumes:
+      - copilot_tokens:/root/.config/litellm/github_copilot
     depends_on:
       db:
         condition: service_healthy
@@ -66,3 +69,4 @@ volumes:
   postgres_data:
   minio_data:
   qdrant_data:
+  copilot_tokens: