devops: fix upload-artifact and use Playwright Docker image for unit tests

- Switch unit-tests job to mcr.microsoft.com/playwright:v1.58.2-noble
  container; Chromium and all system deps are pre-installed so the
  browser install/cache dance is eliminated entirely (closes #13)

- Downgrade upload-artifact@v4 → v3 in both unit-tests and e2e-tests
  jobs; v4 is not supported on Gitea (GHES) and was causing jobs to
  report failure even when all tests passed, and prevented the
  Playwright browser cache from ever being saved (closes #14)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -6,17 +6,16 @@ on:
 
 jobs:
   # ─── Unit & Browser Component Tests ──────────────────────────────────────────
-  # No backend needed — Vitest runs in Node (utils) and headless Chromium (components).
+  # Runs inside the official Playwright Docker image — Chromium and all system
+  # deps are pre-installed, so no install or cache step is needed for the browser.
   unit-tests:
     name: Unit & Component Tests
     runs-on: ubuntu-latest
+    container:
+      image: mcr.microsoft.com/playwright:v1.58.2-noble
     steps:
       - uses: actions/checkout@v4
 
-      - uses: actions/setup-node@v4
-        with:
-          node-version: 20
-
       - name: Cache node_modules
         id: node-modules-cache
         uses: actions/cache@v4
@@ -29,30 +28,13 @@ jobs:
         run: npm ci
         working-directory: frontend
 
-      - name: Cache Playwright browsers
-        id: playwright-cache
-        uses: actions/cache@v4
-        with:
-          path: ~/.cache/ms-playwright
-          key: playwright-chromium-${{ hashFiles('frontend/package-lock.json') }}
-
-      - name: Install Playwright Chromium + system deps
-        if: steps.playwright-cache.outputs.cache-hit != 'true'
-        run: npx playwright install chromium --with-deps
-        working-directory: frontend
-
-      - name: Install Playwright system deps (browser binary already cached)
-        if: steps.playwright-cache.outputs.cache-hit == 'true'
-        run: npx playwright install-deps chromium
-        working-directory: frontend
-
       - name: Run unit and component tests
         run: npm test
         working-directory: frontend
 
       - name: Upload screenshots
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: unit-test-screenshots
           path: frontend/test-results/screenshots/
@@ -207,7 +189,7 @@ jobs:
 
       - name: Upload E2E results
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: e2e-results
           path: frontend/test-results/e2e/