[feat] Add ZIP download support for multiple assets

## Summary
When downloading multiple selected assets, they are now bundled into a single ZIP file instead of downloading each file individually.

## Changes
- Use `client-zip` library to generate ZIP files in the browser
- Use `Promise.allSettled` to include remaining files in ZIP even if some fail
- Automatically add numbers to duplicate filenames
- Notify users with toast messages based on download status
- Auto-generate filename with timestamp to prevent filename collisions

### Modified Files
- `src/platform/assets/composables/useMediaAssetActions.ts`: Implement ZIP download logic
- `src/locales/en/main.json`: Add new i18n strings
- `package.json`: Add `client-zip` dependency

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -159,6 +159,7 @@
     "algoliasearch": "catalog:",
     "axios": "catalog:",
     "chart.js": "^4.5.0",
+    "client-zip": "catalog:",
     "dompurify": "^3.2.5",
     "dotenv": "catalog:",
     "es-toolkit": "^1.39.9",