feat: add extension update check

docs/internal-extension-distribution.md

@@ -13,7 +13,28 @@
 
 1. Run `npm test`.
 2. Run `npm run package:internal`.
-3. Send `release/star-chart-search-enhancer-internal.zip` to coworkers.
+3. Run `npm run write:latest`.
+4. Send `release/star-chart-search-enhancer-internal.zip` to coworkers.
+
+## COS Update Manifest
+
+The popup checks `src/shared/update-config.ts` for the update manifest URL.
+
+Before publishing the COS-based update flow:
+
+1. Upload these files to COS:
+   - `release/latest.json`
+   - `release/star-chart-search-enhancer-internal.zip`
+   - `release/星图增强插件-超简单安装使用指南.pdf`
+2. Make the COS path publicly readable.
+3. Replace the placeholder `UPDATE_MANIFEST_URL` in `src/shared/update-config.ts`.
+4. Rebuild and package the extension.
+
+The release manifest can be generated with a real public base URL:
+
+```bash
+UPDATE_PUBLIC_BASE_URL="https://<your-cos-domain>/star-chart-search-enhancer/releases/<version>" npm run write:latest
+```
 
 ## Coworker Install Steps