Allow customization of worktree branch name prefixes

Allow customization of worktree branch name prefixes

When GitHub Copilot App creates a worktree session, it automatically creates a branch such as:

nishijima267-fantastic-goggles

I would like an option to configure the branch naming format, for example:

copilot/nishijima267/fantastic-goggles

Using a "copilot//" prefix would make it immediately clear that the branch was created by Copilot, identify its owner in shared repositories, and group Copilot branches consistently.

Ideally, this could be configured globally or per project in the App settings.

Repository instructions such as AGENTS.md or .github/copilot-instructions.md cannot solve this because the branch and worktree are created before those instructions are read.

---
| Field | Value |
| --- | --- |
| App version | 1.1.12 |
| OS | Windows 10.0.26200 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Day 2 (Week 1) |

Comienza siguiendo el flujo de creación de GitHub Copilot App worktree session y la generación actual de nombres de ramas; después, inspecciona dónde se definen las App settings globales y por proyecto. Se considera terminado cuando los usuarios pueden configurar un prefijo de rama y las worktree branches recién creadas aplican de forma coherente el formato seleccionado.

Escrito por el modelo de indexación a partir del texto del issue.