feat: Add testing infrastructure and documentation

- Set up Vitest for unit testing with jsdom
- Add test setup with Web Audio API and requestAnimationFrame mocks
- Create initial test suites for DOM and animations modules
- Add test scripts to package.json (test, test:ui, test:run, coverage)
- Update CI workflow to include test execution
- Create CONTRIBUTING.md with conventional commits guidelines
- Create SECURITY.md with security policy
- Update ESLint config to support test files
- All tests passing (8/8)

Co-authored-by: ZaneThePython <102631678+ZaneThePython@users.noreply.github.com>

eslint.config.js

@@ -22,6 +22,7 @@ export default [
         setTimeout: 'readonly',
         setInterval: 'readonly',
         clearInterval: 'readonly',
+        clearTimeout: 'readonly',
         IntersectionObserver: 'readonly',
         __dirname: 'readonly',
       },
@@ -33,6 +34,19 @@ export default [
       'no-var': 'warn',
     },
   },
+  {
+    files: ['tests/**/*.js'],
+    languageOptions: {
+      globals: {
+        global: 'writable',
+        beforeEach: 'readonly',
+        describe: 'readonly',
+        it: 'readonly',
+        expect: 'readonly',
+        vi: 'readonly',
+      },
+    },
+  },
   {
     ignores: [
       'node_modules/**',