Fix NPM integration: correct forward host, SSL, and add UDP stream

- Forward proxy to host IP + dashboard_port instead of container name
- Remove redundant advanced_config (Caddy handles internal routing)
- Add provider: letsencrypt to SSL certificate request
- Add NPM UDP stream creation/deletion for STUN/TURN relay ports
- Add npm_stream_id to Deployment model with migration
- Fix API docs URL in README (/api/docs)

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

README.md

@@ -131,7 +131,7 @@ Per customer instance (5 containers): **~100 MB RAM**
 | Port | Protocol | Purpose |
 |------|----------|---------|
 | 8000 | TCP | NetBird MSP Appliance Web UI |
-| 9000+ | TCP | NetBird Web Management per customer (one per customer, increments by 1) |
+| 9000+ | TCP | NetBird Web Management per customer (only internal, one per customer, increments by 1) |
 | 3478+ | UDP | STUN/TURN relay per customer (one per customer, increments by 1) |
 
 Example for 3 customers:
@@ -330,7 +330,7 @@ curl -X POST http://localhost:8000/api/auth/token \
 
 Full interactive documentation available at:
 ```
-http://your-server:8000/docs
+http://your-server:8000/api/docs
 ```
 
 **Common Endpoints:**