fix: CI/CD test failures and invalid Go version

- Fix go.mod Go version from invalid 1.25.7 to 1.23
- Fix Dockerfile golang image from 1.25 to 1.23
- Add window.matchMedia mock for jsdom themeStore tests
- Exclude e2e/ from Vitest to prevent Playwright test conflicts
- Add frontend test step to both CI workflows

frontend/src/test/setup.ts

@@ -0,0 +1,14 @@
+import '@testing-library/jest-dom/vitest';
+
+// Mock window.matchMedia for themeStore tests
+Object.defineProperty(window, 'matchMedia', {
+  writable: true,
+  value: (query: string) => ({
+    matches: query.includes('prefers-color-scheme: dark') ? false : false,
+    media: query,
+    onchange: null,
+    addEventListener: () => {},
+    removeEventListener: () => {},
+    dispatchEvent: () => {},
+  }),
+});

frontend/vitest.config.mjs

@@ -0,0 +1,22 @@
+import { defineConfig } from 'vitest/config';
+import react from '@vitejs/plugin-react';
+import path from 'path';
+import { fileURLToPath } from 'url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+export default defineConfig({
+  plugins: [react()],
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    setupFiles: ['./src/test/setup.ts'],
+    css: true,
+    exclude: ['e2e/**', 'node_modules/**'],
+  },
+  resolve: {
+    alias: {
+      '@': path.resolve(__dirname, './src'),
+    },
+  },
+});