Distinguish "agent working" vs "awaiting user input" vs "turn complete" in the title-bar indicator

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

I need a visual indicator to distinguish when an agent is performing work and when it is waiting on input.

### Proposed solution

The spinning indicator in the title bar currently means two different things, which makes it hard to know whether Copilot needs me or is actively working:

1. The agent is processing / running tools (legitimate spinner)
2. The agent is blocked waiting for me to respond (e.g., ask_user prompt, permission prompt, or just idle after a turn)

Both look identical, so I sometimes wait on Copilot while Copilot is waiting on me.

Request: A 3-state indicator with distinct glyphs:

| State | Suggested glyph |
|---|---|
| Agent working / running tools | 🔄 (current spinner) |
| Awaiting user input (ask_user, permission, idle post-turn) | ⚠️ |
| Turn just completed successfully | ✅ (briefly, then idle) |

Bonus points if the glyphs are configurable via settings.json or a new /theme key, e.g.:

```json
"indicator": {
"working": "🔄",
"awaiting": "⚠️",
"done": "✅"
}
```

### Example prompts or workflows

_No response_

### Additional context

_No response_

Commencez par retracer l’indicateur de la barre de titre et les transitions d’état pour l’exécution des outils, les invites utilisateur, les permissions et les tours terminés. Définissez et vérifiez des états distincts de travail, d’attente d’entrée et de brièvement terminé ; les glyphes configurables suggérés par l’issue constituent une extension optionnelle. Confirmez que les trois états sont visuellement distinguables dans les workflows concernés.

Rédigé par le modèle d'indexation à partir du texte de l'issue.