feat: add Paperless-ngx document storage integration

- Add /documents router with webhook, upload, search, health endpoints
- Create DocumentSyncService for indexing documents to vectors/graph
- Add PaperlessClient for REST API integration
- Configure dependency injection for Paperless client
- Add document models for webhook payloads and responses
- Event-driven architecture via Paperless workflow webhooks

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/main.py

@@ -51,7 +51,7 @@ app.add_middleware(
 from src.routers import (
     wiki, tools, graph, vector, hybrid_rag, consolidation,
     ingestion, entity_linking, webhooks, rag_search, content,
-    maintenance, volatile
+    maintenance, volatile, documents
 )
 
 app.include_router(wiki.router)
@@ -67,6 +67,7 @@ app.include_router(rag_search.router)
 app.include_router(content.router)
 app.include_router(maintenance.router)
 app.include_router(volatile.router)
+app.include_router(documents.router)
 
 # Mount static files directory for Wiki.js integration scripts
 static_dir = Path(__file__).parent.parent / "static"