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/webui/index.js

@@ -668,10 +668,11 @@ export function mountWebUI(app, dirname, accountManager) {
                         const accountData = await completeOAuthFlow(code, verifier);
 
                         // Add or update the account
+                        // Note: Don't set projectId here - it will be discovered and stored
+                        // in the refresh token via getProjectForAccount() on first use
                         await addAccount({
                             email: accountData.email,
                             refreshToken: accountData.refreshToken,
-                            projectId: accountData.projectId,
                             source: 'oauth'
                         });