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

launcher/src-tauri/src/accounts.rs

@@ -45,10 +45,8 @@ impl AccountsFile {
 
     /// Add or replace (same kind + uuid + panel) and make it active.
     pub fn upsert(&mut self, account: Account) -> Account {
-        if let Some(existing) = self
-            .accounts
-            .iter_mut()
-            .find(|a| a.kind == account.kind && a.uuid == account.uuid && a.panel_url == account.panel_url)
+        if let Some(existing) =
+            self.accounts.iter_mut().find(|a| a.kind == account.kind && a.uuid == account.uuid && a.panel_url == account.panel_url)
         {
             let id = existing.id.clone();
             *existing = Account { id: id.clone(), ..account };