test: Add global mock embedding setup to prevent timeouts

- Create test-setup.ts with global vi.mock for embedding module
- Mock all embedding functions to avoid loading Transformers.js
- Configure vitest to load mock setup before all tests
- Fixes timeout issues in majority of test files

Tests now run significantly faster with deterministic mock embeddings

vitest.config.ts

@@ -4,7 +4,7 @@ export default defineConfig({
   test: {
     // Default configuration
     globals: true,
-    setupFiles: ['./tests/setup.ts'],
+    setupFiles: ['./tests/test-setup.ts', './tests/setup.ts'],
     testTimeout: 120000, // 120 seconds for TensorFlow operations
     hookTimeout: 120000,
     // Run tests in parallel with limited pool