feat(05-07): 3-tab SettingsView, SettingsCloudTab, CloudCredentialModal

- Convert SettingsView to 3-tab layout (Preferences/AI/Cloud) matching AdminView pattern
- Extract SettingsPreferencesTab.vue and SettingsAiTab.vue from original SettingsView
- Create SettingsCloudTab.vue with all 4 providers, status badges, action buttons
- Create CloudCredentialModal.vue for WebDAV/Nextcloud credential input
- Handle OAuth callback query params (cloud_connected/cloud_error) in SettingsView.onMounted
- Add success toast (auto-dismiss 5s) and persistent error banner for OAuth results
- Fix pre-existing build failure: add build.target=esnext to vite.config.js for top-level await support
- 2 SettingsCloudTab mount tests passing (W4 — CLAUDE.md)

frontend/vite.config.js

@@ -3,6 +3,10 @@ import vue from '@vitejs/plugin-vue'
 
 export default defineConfig({
   plugins: [vue()],
+  build: {
+    // top-level await in main.js requires esnext target
+    target: 'esnext',
+  },
   server: {
     host: '0.0.0.0',
     port: 5173,