Implement sidecar video thumbnails and improved processing UI

- Implemented "sidecar" thumbnail logic: imports video thumbnails from Google Photos as hidden Drive files to display immediately while videos process.
- Updated MediaService to serve sidecar thumbnails via server-side Base64 encoding, bypassing CORS restrictions.
- Implemented lifecycle management: detects video processing completion to automatically cleanup sidecar files and fallback to native Drive thumbnails.
- Enhanced Media Manager UI: added processing warning banner and refined processing tile styling (centered, lighter overlay).
- Upgraded Drive API to v3 and improved file creation robustness with Advanced API fallbacks.

src/services/MockDriveService.ts

@@ -43,23 +43,33 @@ export class MockDriveService implements IDriveService {
 
   saveFile(blob: GoogleAppsScript.Base.Blob, folderId: string): GoogleAppsScript.Drive.File {
      const id = `mock_file_${Date.now()}_${Math.floor(Math.random() * 1000)}`
+
      const newFile = {
         getId: () => id,
         getName: () => blob.getName(),
         getBlob: () => blob,
         getUrl: () => `https://mock.drive/files/${blob.getName()}`,
         getLastUpdated: () => new Date(),
-        getThumbnail: () => ({ getBytes: () => [] }),
+        getThumbnail: () => (blob as any).getThumbnail ? (blob as any).getThumbnail() : ({ getBytes: () => [] }),
         getMimeType: () => (blob as any).getContentType ? (blob as any).getContentType() : "image/jpeg",
         getDownloadUrl: () => `https://drive.google.com/uc?export=download&id=${id}`,
         getSize: () => blob.getBytes ? blob.getBytes().length : 0,
-        getAppProperty: (key) => {
-             return (newFile as any)._properties?.[key]
-        }
+        getAppProperty: (key) => (newFile as any)._properties?.[key],
+        // Placeholder methods to be overridden safely
+        setDescription: null as any,
+        getDescription: null as any
      } as unknown as GoogleAppsScript.Drive.File
 
-     // Initialize properties container
-     ;(newFile as any)._properties = {}
+     // Initialize state
+     ;(newFile as any)._properties = {};
+     ;(newFile as any)._description = "";
+
+     // Attach methods safely
+     newFile.setDescription = (desc: string) => {
+         (newFile as any)._description = desc;
+         return newFile;
+     };
+     newFile.getDescription = () => (newFile as any)._description || "";
 
      if (!this.files.has(folderId)) {
         this.files.set(folderId, [])