Fix game bugs and add comprehensive test suite with CI

Bug fixes:
- Remove undeclared `mistakes` variable in sentence-builder (implicit global)
- Reset timer bar width/text/color on speed-quiz restart
- Update aria-valuenow on progress bars across all 6 games
- Add aria-live="polite" to flashcards flip prompt

Test suite (158 tests):
- Data integrity: words, sentences, verbs, accents, fill-the-gap validation
- Build output: pages exist, SEO meta, links, images, accessibility, game structure
- GitHub Actions CI workflow on push/PR to main

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mrtnzlml

.github/workflows/ci.yml

@@ -0,0 +1,21 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+
+      - run: npm ci
+      - run: npm test