fix: inline video upload in artefacts — drop modal, add drag-and-drop + progress bar

- Replace the two-step video modal with inline drag-and-drop zone + click-to-browse
- Add Google Drive URL input directly in the versions tab
- Add upload progress bar with percentage via XHR
- Support onUploadProgress in api.upload()

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/src/i18n/en.json

@@ -849,6 +849,7 @@
   "artefacts.uploadFile": "Upload File",
   "artefacts.chooseVideoFile": "Choose video file",
   "artefacts.videoFormats": "MP4, MOV, AVI, etc.",
+  "artefacts.dropOrClickVideo": "Drop a video here or click to browse",
   "artefacts.googleDriveLink": "Google Drive Link",
   "artefacts.googleDriveUrl": "Google Drive URL",
   "artefacts.driveUrlPlaceholder": "https://drive.google.com/file/d/...",