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) |

Start by tracing the GitHub Copilot App worktree session creation flow and the current branch-name generation, then inspect where global and per-project App settings are defined. Done means users can configure a branch prefix and newly created worktree branches consistently apply the selected format.

Written by the indexing model from the issue text.