feat(cd): add Matrix notification on deploy failure

Sends a message to a Matrix room when a deploy fails, including
the failing services, commit, deployer, and a link to the logs.

Requires two GitHub Actions secrets:
- DEPLOY_NOTIFY_ROOM_ID: Matrix room ID
- DEPLOY_NOTIFY_BOT_TOKEN: Matrix bot access token

Skips silently if secrets are not configured.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

games/whopixels/css/style.css

@@ -0,0 +1,14 @@
+body {
+    margin: 0;
+    padding: 0;
+    background-color: #000;
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    height: 100vh;
+    font-family: 'Arial', sans-serif;
+}
+
+#game-container {
+    box-shadow: 0 0 10px rgba(255, 255, 255, 0.2);
+}