Refactor to LiamAEdwards watchdog approach

- Dockerfile: Download server from wylab CDN at build time, build watchdog
- start.sh: Simplified to copy defaults and run watchdog
- appsettings.yml: Configure for wylab instance with CDN manifest
- main.yml: Simplified workflow with auto-tagging via metadata-action
- Delete update_build_metadata.py (no longer needed)

Based on: https://github.com/LiamAEdwards/SS14-Docker-Linux-Server

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

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

start.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+# Copy default files to volume on first run
+if [ ! "$(ls -A /ss14)" ]; then
+    cp -r /ss14-default/* /ss14/
+fi
+
+# Run watchdog
+cd /ss14/publish/
+exec ./SS14.Watchdog "$@"