fix: enable CI on feature branches and add workflow_dispatch

The original ci.yaml only triggered on push to main, meaning pushes to
feature branches (like argocd#8) never triggered CI.

Changes:
- Change push trigger from 'branches: [main]' to 'branches: ["**"]'
  so pushes to any branch trigger CI
- Add workflow_dispatch for manual trigger capability
- Keep pull_request trigger for PR-based runs
- Preserve simple reusable workflow pattern

Fixes PRI-524: GitHub Actions CI not re-triggering on argocd#8 branch.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yaml

@@ -2,9 +2,13 @@ name: CI
 
 on:
   push:
-    branches: [main]
+    branches: ['**']
   pull_request:
     branches: [main]
+  workflow_dispatch:
+
+permissions:
+  contents: read
 
 jobs:
   ci: