Session creation fails when git remote is not named "origin"

Session creation fails when git remote is not named "origin"

When a project's git remote pointing to the correct GitHub repo is named something other than `origin` (e.g., `savvy-trader`), session creation fails with "has no origin remote." The app itself added the project using this remote, so it should use whichever remote matches the configured repo URL, not hardcode `origin`

---
| Field | Value |
| --- | --- |
| App version | 1.1.13 |
| OS | macOS 26.5.2 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Day 1 |

Start from session creation on the /chat path and trace how the configured repository URL is matched to a git remote. Verify the behavior with a project whose matching remote is not named origin; done means session creation succeeds using the remote that matches the configured GitHub repository URL.

索引モデルが issue の本文から書いたものです。