feat: add testing infrastructure and improve component feedback

- Added React testing setup with JSDOM
- Added component tests for AddTransactionForm and TransactionTable
- Improved error handling and success messages in components
- Updated test configuration and dependencies
- Added CSS for error and success states

vitest.config.ts

@@ -1,21 +1,27 @@
 /// <reference types="vitest" />
+import react from '@vitejs/plugin-react';
 import { defineConfig } from 'vitest/config';
 
 export default defineConfig({
+  plugins: [react()],
   test: {
-    // Increase timeout for slower CI environments
-    testTimeout: 10000,
-    // Use the setup file we created
+    // Ensure non-interactive and CI-friendly configuration
+    watch: false,
+    silent: false,
+    passWithNoTests: true,
+    teardownTimeout: 5000,
+    // Testing environment setup
+    environment: 'jsdom',
     setupFiles: ['./src/test/setup.ts'],
-    // Ensure we're using the right environment
-    environment: 'node',
-    // Only include test files
-    include: ['src/test/**/*.{test,spec}.{ts,js}'],
-    // Configure coverage collection
+    // Test file patterns
+    include: ['src/test/**/*.{test,spec}.{ts,tsx}'],
+    // Coverage configuration
     coverage: {
       provider: 'v8',
       reporter: ['text', 'json', 'html'],
       exclude: ['node_modules/', 'src/test/**/*', '**/*.d.ts'],
     },
+    // Global settings
+    globals: true,
   },
 });