Fix duplicate media import bug and rename MediaSidebar to MediaManager

- Renamed src/MediaSidebar.html to src/MediaManager.html to align with modal UI.
- Fixed race condition in Photo Picker polling preventing duplicate imports.
- Updated global.ts, initMenu.ts, and mediaHandlers.ts used in the fix.
- Fixed unit tests for mediaHandlers.

src/mediaHandlers.ts

@@ -7,11 +7,12 @@ import { Shop } from "./shopifyApi"
 import { Config } from "./config"
 import { Product } from "./Product"
 
-export function showMediaSidebar() {
-  const html = HtmlService.createHtmlOutputFromFile("MediaSidebar")
+export function showMediaManager() {
+  const html = HtmlService.createHtmlOutputFromFile("MediaManager")
     .setTitle("Media Manager")
-    .setWidth(350);
-  SpreadsheetApp.getUi().showSidebar(html);
+    .setWidth(1100)
+    .setHeight(750);
+  SpreadsheetApp.getUi().showModalDialog(html, "Media Manager");
 }
 
 export function getSelectedSku(): string | null {