Add Docker + nginx deployment for homelab

- Multi-stage Dockerfile: Node builds static assets, nginx serves them
- nginx proxies /api/* to football-data.org and injects X-Auth-Token
  server-side via FOOTBALL_API_KEY env var (key never in browser bundle)
- docker-compose.yml exposes the app on port 3000
- Extract apiFetch() helper: sends key in dev (Vite proxy), skips in prod
- .env.example updated with both dev and production key vars

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

src/api.js

@@ -0,0 +1,11 @@
+// In dev, Vite proxies /api/* but doesn't inject the key, so we send it
+// from the browser. In production the nginx proxy injects it server-side.
+const DEV_KEY = import.meta.env.VITE_FOOTBALL_API_KEY
+
+export function apiFetch(path) {
+  const headers = DEV_KEY ? { 'X-Auth-Token': DEV_KEY } : {}
+  return fetch(`/api${path}`, { headers }).then((res) => {
+    if (!res.ok) throw new Error(`API error: ${res.status} ${res.statusText}`)
+    return res.json()
+  })
+}