Add Vitest testing framework with initial test suites

- Install vitest as dev dependency
- Add vitest.config.js configuration
- Add conditional exports to src/assets/js/games/config.js for testability
- Create tests/config.test.mjs with 14 tests for game config module
- Create tests/eleventy-config.test.mjs with 13 tests for Eleventy config
- Create tests/build-data.test.mjs with 5 tests for build data module
- Add test and test:watch scripts to package.json
- Add .github/workflows/tests.yml CI workflow

Agent-Logs-Url: https://github.com/NextCommunity/NextCommunity.github.io/sessions/58354e39-729b-4d04-8d52-2b31f4f40012

Co-authored-by: jbampton <418747+jbampton@users.noreply.github.com>

Author: Copilot

.github/workflows/tests.yml

@@ -0,0 +1,30 @@
+name: Tests
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+permissions: {}
+
+jobs:
+  test:
+    name: Run Tests
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - name: Checkout Code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - name: Setup Node.js
+        uses: actions/setup-node@53b83947a5a98c8d113130e565377fae1a50d02f # v6.3.0
+        with:
+          node-version: 24
+          cache: npm
+      - name: Install dependencies
+        run: npm ci
+      - name: Run tests
+        run: npm test