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/config.py

@@ -101,6 +101,11 @@ class Settings(BaseSettings):
     content_extraction_timeout: int = Field(default=5, ge=1, le=30, description="Trafilatura per-URL timeout in seconds")
     content_max_length: int = Field(default=2000, ge=500, le=10000, description="Max extracted content length per result")
 
+    # Paperless-ngx Configuration
+    paperless_url: str = Field(default="http://paperless:8000", description="Paperless-ngx URL")
+    paperless_token: str = Field(default="", description="Paperless-ngx API token")
+    paperless_timeout: int = Field(default=30, ge=5, le=120, description="Paperless API timeout in seconds")
+
     # Document Store Configuration
     document_store_enabled: bool = Field(default=True, description="Enable document store feature")
     document_catalog_path_prefix: str = Field(default="docs", description="Wiki path prefix for catalog pages")