fix: prevent codex spawn error when codex CLI is not installed

Return success with empty servers array from the config read endpoint
when no config file exists, so the frontend doesn't fall through to
the CLI list endpoint which attempts to spawn the codex binary.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server/routes/codex.js

@@ -262,7 +262,7 @@ router.get('/mcp/config/read', async (req, res) => {
     }
 
     if (!configData) {
-      return res.json({ success: false, message: 'No Codex configuration file found', servers: [] });
+      return res.json({ success: true, servers: [] });
     }
 
     const servers = [];