Trigger CI on ci/* branches so main can stay protected

.gitea/workflows/build.yaml

@@ -14,7 +14,8 @@ name: Build RPi image
 
 on:
   push:
-    branches: [main]
+    # main is release-protected; CI branches may be pushed freely for testing
+    branches: [main, 'ci/*']
   workflow_dispatch:
 
 # Never run two builds at once on the same (single) runner.