Add PDF document service with AI extraction and per-app settings

- New `features/doc-service` FastAPI microservice: PDF upload, async
  text extraction (pdfplumber), AI classification via Anthropic/Ollama/
  LM Studio, per-user categories, file download
- Alembic migration isolated with `alembic_version_doc_service` table
- Main backend: httpx proxy routers for /api/documents/* and
  /api/documents/categories/*, admin settings API at /api/settings/*
- Runtime config in /config/doc_service_config.json (shared Docker
  volume); api_key masking on reads; atomic write with os.replace()
- Frontend: DocumentsPage, DocumentAdminSettingsPage, updated AppsPage
  launcher hub, simplified Nav (removed Settings link), new routes
- docker-compose: doc-service service, doc_data + app_config volumes,
  removed internal:true from backend-net for outbound AI API calls
- Fix pre-commit hook: probe Docker socket path so git subprocess picks
  up Docker Desktop on macOS
- Fix security_check.py: use sys.executable for bandit so venv python
  is used instead of system python

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

features/doc-service/app/services/ai/__init__.py

@@ -0,0 +1,23 @@
+from app.services.ai.base import AIProvider
+
+
+def get_provider(ai_config: dict) -> AIProvider:
+    """
+    Factory: return an AIProvider instance based on the 'provider' key in the AI config section.
+    ai_config is the 'ai' section of doc_service_config.json, loaded fresh per processing job.
+    """
+    provider_name = ai_config.get("provider", "anthropic")
+    provider_cfg = ai_config.get(provider_name, {})
+
+    match provider_name:
+        case "anthropic":
+            from app.services.ai.anthropic_provider import AnthropicProvider
+            return AnthropicProvider(provider_cfg)
+        case "ollama" | "lmstudio":
+            from app.services.ai.openai_compat import OpenAICompatProvider
+            return OpenAICompatProvider(provider_cfg)
+        case _:
+            raise ValueError(f"Unknown AI provider: {provider_name!r}")
+
+
+__all__ = ["AIProvider", "get_provider"]