ci: add build + vulnerability check for PRs (gates Renovate auto-merge)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Hs9HXPWVtqDukF9MbJKbpw

.gitea/workflows/ci.yml

@@ -0,0 +1,40 @@
+name: CI
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    env:
+      DALAMUD_HOME: /tmp/dalamud
+      PROJECT: CustomizePlus/CustomizePlus.csproj
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+      - uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: 10.0.x
+      - name: Download Dalamud
+        run: |
+          wget -q https://goatcorp.github.io/dalamud-distrib/latest.zip -O "$DALAMUD_HOME.zip"
+          unzip -q "$DALAMUD_HOME.zip" -d "$DALAMUD_HOME"
+      - name: Restore
+        run: dotnet restore "$PROJECT"
+      - name: Build
+        run: dotnet build --configuration Release "$PROJECT" --no-restore
+      - name: Fail on vulnerable packages
+        run: |
+          out=$(dotnet list "$PROJECT" package --vulnerable --include-transitive 2>&1)
+          echo "$out"
+          if echo "$out" | grep -qi 'has the following vulnerable'; then
+            echo "::error::Vulnerable packages detected"; exit 1
+          fi