feat: align project discovery with opencode-antigravity-auth reference

- Store project IDs in composite refresh token format (refreshToken|projectId|managedProjectId)
- Add parseRefreshParts() and formatRefreshParts() for token handling
- Extract and persist subscription tier during project discovery
- Fetch subscription in blocking mode when missing from cached accounts
- Fix conditional duetProject setting to match reference implementation
- Export parseTierId() for reuse across modules

Co-Authored-By: Claude <noreply@anthropic.com>

src/account-manager/index.js

@@ -297,7 +297,8 @@ export class AccountManager {
      * @returns {Promise<string>} Project ID
      */
     async getProjectForAccount(account, token) {
-        return fetchProject(account, token, this.#projectCache);
+        // Pass onSave callback to persist managedProjectId in refresh token
+        return fetchProject(account, token, this.#projectCache, () => this.saveToDisk());
     }
 
     /**