refactor(oauth): align box chars with CCS standard and add JSDoc

Use Unicode box characters (╔═╗║╚╝) per design guidelines and
add JSDoc to parseCallbackUrl helper function.

src/cliproxy/auth/oauth-handler.ts

@@ -241,9 +241,9 @@ async function handlePasteCallbackMode(
 
     // Display auth URL in box
     console.log('');
-    console.log('  +--------------------------------------------------------------+');
+    console.log('  ╔══════════════════════════════════════════════════════════════╗');
-    console.log('  |  Open this URL in any browser:                               |');
+    console.log('  ║  Open this URL in any browser:                               ║');
-    console.log('  +--------------------------------------------------------------+');
+    console.log('  ╚══════════════════════════════════════════════════════════════╝');
     console.log('');
     console.log(`    ${authUrl}`);
     console.log('');

src/web-server/routes/cliproxy-auth-routes.ts

@@ -630,7 +630,9 @@ router.get('/:provider/status', async (req: Request, res: Response): Promise<voi
 });
 
 /**
- * Parse callback URL to extract code and state parameters.
+ * Parse OAuth callback URL to extract code and state parameters.
+ * @param url - The callback URL to parse
+ * @returns Parsed components (code, state) or empty object on failure
  */
 function parseCallbackUrl(url: string): { code?: string; state?: string } {
   try {