feat(media): implement integrated media manager with sidebar and picker

- Implement DriveService and ShopifyMediaService for backend operations
- Create MediaSidebar.html with premium UI and auto-polling
- Integrate Google Picker API for robust file selection
- Orchestrate sync logic via MediaService (Drive -> Staged Upload -> Shopify)
- Add secure config handling for API keys and tokens
- Update ppsscript.json with required OAuth scopes
- Update MEMORY.md and README.md with architecture details

src/services/GASNetworkService.ts

@@ -0,0 +1,7 @@
+import { INetworkService } from "../interfaces/INetworkService"
+
+export class GASNetworkService implements INetworkService {
+  fetch(url: string, params: GoogleAppsScript.URL_Fetch.URLFetchRequestOptions): GoogleAppsScript.URL_Fetch.HTTPResponse {
+    return UrlFetchApp.fetch(url, params)
+  }
+}