There should be a filter for those who have a LOT of session repos

When a user has a large number of session repositories loaded within github app, it can be difficult to manage.

Request: There ought to be a very simple UI based sorting and filtering set of controls, that includes a filter by name (via substring)

Example of the issue:

---
| Field | Value |
| --- | --- |
| App version | 1.0.26 |
| OS | macOS 26.5.1 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Week 6 |

Start from the /chat view where session repositories are loaded and inspect the existing repository-list UI. Add simple sorting and filtering controls, including substring matching by name, then verify that users can narrow and manage a large repository list.

索引モデルが issue の本文から書いたものです。