Rename should show the name at all times

### Describe the feature or problem you'd like to solve

When you "rename" a session in Claude Code it shows it all the time so it's obvious what session you're. Copilot CLI should do the same.

### Proposed solution

```
────────────────────────────────────────────────────────────────────────────────────────────────────────My Session──
❯
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
ctrl+c / right-click copy GPT-5.5
```

### Example prompts or workflows

_No response_

### Additional context

_No response_

No files, tests, or entry points are named. Start by reproducing a renamed session in Copilot CLI and inspect the current terminal layout; done means the session name remains visible throughout the interface as shown in the proposed mockup.

Written by the indexing model from the issue text.