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) |

Beginne damit, den Ablauf der Erstellung einer GitHub Copilot App worktree session und die aktuelle Generierung von Branchnamen nachzuverfolgen, und untersuche anschließend, wo globale und projektspezifische App-Einstellungen definiert sind. Die Aufgabe ist abgeschlossen, wenn Benutzer ein Branch-Präfix konfigurieren können und neu erstellte worktree branches das ausgewählte Format konsistent anwenden.

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