Refactor Media Manager UI and Fix Infinite Loop

- **UI Refactor**:
  - Split Media Manager header into two distinct cards: 'Product Info' and 'Upload Options'.
  - 'Product Info' now displays the Product Title and SKU.
  - Renamed upload buttons to 'Google Drive', 'Google Photos', and 'Your Computer' for clarity.
  - Added global drag-and-drop support with overlay.
  - Replaced full-screen 'Connecting' overlay with an inline spinner for better UX and log visibility.

- **Backend**:
  - Renamed getSelectedSku to getSelectedProductInfo in mediaHandlers.ts to fetch and return both SKU and Title.
  - Updated global.ts exports and mediaHandlers.test.ts to support the new signature.

- **Fixes**:
  - Resolved an infinite loop issue in loadMedia caused by incorrect SKU state handling.

src/mediaHandlers.ts

@@ -15,7 +15,7 @@ export function showMediaManager() {
   SpreadsheetApp.getUi().showModalDialog(html, "Media Manager");
 }
 
-export function getSelectedSku(): string | null {
+export function getSelectedProductInfo(): { sku: string, title: string } | null {
   const ss = new GASSpreadsheetService()
   const sheet = SpreadsheetApp.getActiveSheet()
   if (sheet.getName() !== "product_inventory") return null
@@ -24,7 +24,9 @@ export function getSelectedSku(): string | null {
   if (row <= 1) return null // Header
 
   const sku = ss.getCellValueByColumnName("product_inventory", row, "sku")
-  return sku ? String(sku) : null
+  const title = ss.getCellValueByColumnName("product_inventory", row, "title")
+
+  return sku ? { sku: String(sku), title: String(title || "") } : null
 }
 
 export function getPickerConfig() {