feat: add Dolphin traversal server for GameCube/Wii netplay

Self-hosted NAT hole-punching relay for Dolphin emulator netplay.
Enables online play for ALL GameCube and Wii games without players
needing to open ports (Mario Party 4-7, MKDD, Smash Melee, etc).

Multi-stage Docker build compiles only the traversal_server target.
UDP ports 6262 (primary) and 6226 (NAT probe).

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

docker/docker-compose.dev.yml

@@ -214,6 +214,20 @@ services:
         limits:
           memory: 128M
 
+  dolphin-traversal:
+    build:
+      context: ../servers/dolphin-traversal
+      dockerfile: Dockerfile
+    container_name: dolphin-traversal
+    restart: unless-stopped
+    ports:
+      - "6262:6262/udp"
+      - "6226:6226/udp"
+    deploy:
+      resources:
+        limits:
+          memory: 64M
+
 volumes:
   postgres_data:
   minio_data: