Add Docker image, Compose, CI/CD workflows and docs

- Multi-arch (amd64/arm64) panel image: static musl binary on scratch,
  cross-compiled with cargo-zigbuild (no QEMU), non-root, healthcheck
- docker-compose.yml + .env.example for one-command deployment
- CI: fmt, clippy, tests, web type-checks, Windows launcher build,
  real-network installs of vanilla/Fabric/Quilt/Forge/NeoForge,
  Docker build
- Release: Windows NSIS installer with baked-in panel URL, GHCR image
  push and GitHub release (tag push or manual dispatch)
- README, admin guide, Microsoft auth setup, architecture, development
- rustfmt config and formatting pass

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011ARcGWxLx21FwXJ3yfGriS

panel/server/src/main.rs

@@ -30,7 +30,9 @@ async fn main() -> anyhow::Result<()> {
 }
 
 async fn shutdown() {
-    let ctrl_c = async { tokio::signal::ctrl_c().await.ok(); };
+    let ctrl_c = async {
+        tokio::signal::ctrl_c().await.ok();
+    };
     #[cfg(unix)]
     let term = async {
         if let Ok(mut s) = tokio::signal::unix::signal(tokio::signal::unix::SignalKind::terminate()) {