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>

app/database.py

@@ -79,6 +79,7 @@ def _run_migrations() -> None:
         ("system_config", "branding_subtitle", "TEXT DEFAULT 'Multi-Tenant Management Platform'"),
         ("system_config", "default_language", "TEXT DEFAULT 'en'"),
         ("users", "default_language", "TEXT"),
+        ("deployments", "npm_stream_id", "INTEGER"),
     ]
     for table, column, col_type in migrations:
         if not _has_column(table, column):