fix: CI workflow now triggers on push to main, clean checkout

The workflow was workflow_dispatch ONLY — pushes never triggered builds.
Every ISO was built from whatever commit was current when someone
manually triggered the workflow from Gitea UI.

Changes:
- Add on.push.branches: [main] trigger
- Set clean: true on checkout to prevent stale cached code

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

.gitea/workflows/build-iso.yml

@@ -1,6 +1,8 @@
 name: Build Archipelago ISO
 
 on:
+  push:
+    branches: [main]
   workflow_dispatch:
 
 jobs:
@@ -12,7 +14,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           fetch-depth: 1
-          clean: false
+          clean: true
 
       - name: Build backend
         run: |