feat(media): Optimize Media Manager loading performance

Significant performance improvements to the 'Loading media...' phase:
- Reduced client-server round trips by consolidating the initial handshake (diagnostics + media fetch) into a single backend call: getMediaManagerInitialState.
- Implemented batched Google Drive metadata retrieval in GASDriveService using the Advanced Drive API, eliminating per-file property fetching calls.
- Switched to HtmlService templates in showMediaManager to pass initial SKU/Title data directly, enabling the UI shell to appear instantly upon opening.
- Updated documentation (ARCHITECTURE.md, MEMORY.md) to clarify Webpack global assignment requirements for GAS functions.
- Verified with comprehensive updates to unit and integration tests.

src/mediaHandlers.ts

@@ -8,7 +8,14 @@ import { Config } from "./config"
 import { Product } from "./Product"
 
 export function showMediaManager() {
-  const html = HtmlService.createHtmlOutputFromFile("MediaManager")
+  const productInfo = getSelectedProductInfo();
+  const template = HtmlService.createTemplateFromFile("MediaManager");
+
+  // Pass variables to template
+  (template as any).initialSku = productInfo ? productInfo.sku : "";
+  (template as any).initialTitle = productInfo ? productInfo.title : "";
+
+  const html = template.evaluate()
     .setTitle("Media Manager")
     .setWidth(1100)
     .setHeight(750);
@@ -193,6 +200,62 @@ export function getMediaDiagnostics(sku: string) {
   }
 }
 
+
+export function getMediaManagerInitialState(providedSku?: string, providedTitle?: string): {
+  sku: string | null,
+  title: string,
+  diagnostics: any,
+  media: any[],
+  token: string
+} {
+  let sku = providedSku;
+  let title = providedTitle || "";
+
+  if (!sku) {
+    const info = getSelectedProductInfo();
+    if (info) {
+      sku = info.sku;
+      title = info.title;
+    }
+  }
+
+  if (!sku) {
+      return {
+          sku: null,
+          title: "",
+          diagnostics: null,
+          media: [],
+          token: ScriptApp.getOAuthToken()
+      }
+  }
+
+  const config = new Config()
+  const driveService = new GASDriveService()
+  const shop = new Shop()
+  const shopifyMediaService = new ShopifyMediaService(shop)
+  const networkService = new GASNetworkService()
+  const mediaService = new MediaService(driveService, shopifyMediaService, networkService, config)
+
+  // Resolve Product ID
+  const product = new Product(sku)
+  try {
+      product.MatchToShopifyProduct(shop);
+  } catch (e) {
+      console.warn("MatchToShopifyProduct failed", e);
+  }
+
+  const shopifyId = product.shopify_id || ""
+  const initialState = mediaService.getInitialState(sku, shopifyId);
+
+  return {
+    sku,
+    title,
+    diagnostics: initialState.diagnostics,
+    media: initialState.media,
+    token: ScriptApp.getOAuthToken()
+  }
+}
+
 export function linkDriveFileToShopifyMedia(sku: string, driveId: string, shopifyId: string) {
   const config = new Config()
   const driveService = new GASDriveService()