Worktree creation fails with lapsed SSO authorization (SAML 403).

Worktree creation fails with lapsed SSO authorization (SAML 403). The app gives misleading error message ("directory does not exist") - it should instead help the user correct the situation (reauthorize)

---
| Field | Value |
| --- | --- |
| App version | 1.0.23 |
| OS | Windows 10.0.26200 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 6 |

Start by reproducing worktree creation from the /chat path with a lapsed SSO authorization on Windows 10, using the reported app version as a reference. Trace how the SAML 403 is translated into the current “directory does not exist” message. Done means the user is told to reauthorize instead of receiving the misleading directory error.

索引モデルが issue の本文から書いたものです。