chore: add sonnet-4-6 mapping, config defaults, and CI improvements

- Add claude-sonnet-4-6 to default Antigravity model mapping
- Add antigravity_extra_retries default value in config
- Add cache-dependency-path to CI setup-go for faster builds
- Simplify vitest config to avoid vite plugin compatibility issues

frontend/vitest.config.ts

@@ -1,18 +1,13 @@
 import { defineConfig } from 'vitest/config'
-import vue from '@vitejs/plugin-vue'
 import { resolve } from 'path'
 
 export default defineConfig({
-  plugins: [vue()],
   resolve: {
     alias: {
       '@': resolve(__dirname, 'src'),
       'vue-i18n': 'vue-i18n/dist/vue-i18n.runtime.esm-bundler.js'
     }
   },
-  define: {
-    __INTLIFY_JIT_COMPILATION__: true
-  },
   test: {
     globals: true,
     environment: 'jsdom',
@@ -37,8 +32,6 @@ export default defineConfig({
           lines: 80
         }
       }
-    },
-    setupFiles: ['./src/__tests__/setup.ts'],
-    testTimeout: 10000
+    }
   }
 })