ci: add helm lint and template validation on PRs

Runs helm lint and helm template for all charts on pull requests
that touch files under charts/. Catches template rendering errors
before merge.

Uses the same Helm version (v3.12.0) and setup action as release.yaml.

Author: Campbell Pool

.github/workflows/ci.yml

@@ -0,0 +1,34 @@
+name: CI
+
+on:
+  pull_request:
+    branches:
+      - main
+    paths:
+      - 'charts/**'
+
+jobs:
+  lint-and-template:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Helm
+        uses: azure/setup-helm@v4
+        with:
+          version: v3.12.0
+
+      - name: Lint charts
+        run: |
+          for chart in charts/*/; do
+            echo "=== Linting ${chart} ==="
+            helm lint "${chart}"
+          done
+
+      - name: Template charts
+        run: |
+          for chart in charts/*/; do
+            echo "=== Templating ${chart} ==="
+            helm template test "${chart}"
+          done