feat(monitor): add STALE state for push monitors

New intermediate state between LATE and DOWN at the midpoint of
the grace period. Gives operators earlier warning that a push
monitor has gone quiet. Includes dedicated orange theme color
across all 5 themes and proper styling in dashboard, detail
panel, and history view.

.gitea/workflows/ci.yml

@@ -1,6 +1,8 @@
 name: CI
 
 on:
+  push:
+    branches: [main]
   pull_request:
 
 env: