ci(portal-self-service): Nx frontend lane (lint/test/build) (refs #65)

Add a make frontend target (pnpm install --frozen-lockfile + nx run-many -t lint
test build) and a CI 'frontend' job (pnpm + Node 24, pinned action URLs). Wire
frontend into make ci. The .NET lanes are unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yaml

@@ -43,6 +43,20 @@ jobs:
           dotnet-version: '10.0.x'
       - run: make unit
 
+  # Frontend (Nx/Angular) lane: install with pnpm, then Nx lint + test + build.
+  frontend:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: https://github.com/actions/checkout@v4
+      - uses: https://github.com/pnpm/action-setup@v4
+        with:
+          version: 11
+      - uses: https://github.com/actions/setup-node@v4
+        with:
+          node-version: '24'
+          cache: 'pnpm'
+      - run: make frontend
+
   mutation:
     runs-on: ubuntu-latest
     steps: