Fix Shopify video previews and various improvements

- Ensure Shopify video sync updates Media Manager with active video previews
- Fix "Image load failed" error for video icons by using Base64 SVG
- Resolve Drive picker origin error by using google.script.host.origin
- Fix Drive video playback issues by using Drive iframe player
- Add `test:log` script to package.json for full output logging in Windows
- Update .gitignore to exclude coverage, test_output.txt, and .agent/
- Remove test_output.txt from git tracking

.gitignore

@@ -3,4 +3,6 @@ dist/**
 desktop.ini
 .continue/**
 .clasp.json
-coverage/
+coverage/
+test_output.txt
+.agent/