Add shared ai-service container as AI provider intermediary

All feature containers now POST messages to ai-service (port 8010) instead
of calling AI providers directly. ai-service routes to LM Studio, Ollama,
or Anthropic based on /config/ai_service_config.json. doc-service AI
providers removed; replaced by httpx ai_client.py. Backend settings
restructured to /api/settings/ai. Frontend gets dedicated AIAdminSettingsPage
and AI Service card in AppsPage.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.dev.yml

@@ -23,8 +23,14 @@ services:
       - ./frontend:/app
       - /app/node_modules
 
+  ai-service:
+    command: sh scripts/start_dev.sh
+    env_file: ./features/ai-service/.env   # gitignored — holds LM Studio / AI credentials
+    volumes:
+      - ./features/ai-service:/app
+
   doc-service:
     command: sh scripts/start_dev.sh
-    env_file: ./features/doc-service/.env   # gitignored — holds local AI credentials
+    env_file: ./features/doc-service/.env
     volumes:
       - ./features/doc-service:/app