Show message timestamps in GitHub Copilot CLI conversations

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

GitHub Copilot CLI doesn't show when each prompt or response occurred, making it hard to tell when something was asked or answered and whether a session was interrupted.

### Proposed solution

Display a timestamp for each turn (user prompt and Copilot response) in the CLI transcript.

• Show a compact local-time stamp per message (e.g.,  [09:47]  or  [2026-06-25 09:47] ), respecting the user's timezone.
• Optionally insert a time-gap separator when a significant interval elapses between turns (e.g.,  — 3 hours later — ), so interruptions and resumed sessions are obvious when scrolling back.
• Make it configurable (on/off, relative vs. absolute, time vs. date+time) via a CLI flag or setting.
• Include timestamps when a session is resumed so the boundary between old and new turns is clear.

### Example prompts or workflows

• Resumed session: I run a task in the morning, step away, and resume the CLI hours later — timestamps immediately show the gap and that the last answer is stale.
• Scheduled/recurring prompts: A scheduled prompt posts updates into the session; timestamps confirm exactly when each run executed and replied.
• Operational debugging: Correlating Copilot CLI suggestions with deployment and log timestamps to reconstruct an accurate timeline.

### Additional context

• The CLI already runs long-lived and resumable sessions where timing context matters most, yet that information isn't surfaced.
• A compact, optional timestamp keeps the terminal output clean while preserving precision when needed.
• This is primarily a UX enhancement; the timing data already exists at message creation time.

Commencez par suivre le rendu des transcriptions de GitHub Copilot CLI et le flux de reprise des sessions, puis identifiez où les heures de création des messages sont disponibles. Vérifiez comment les flags ou les paramètres de CLI sont définis avant de décider comment configurer l’affichage des horodatages et les séparateurs d’intervalle de temps. Le travail est considéré comme terminé lorsque les conversations reprises et planifiées affichent des tours avec les bons horaires, sans rendre la sortie du terminal par défaut inutilement chargée.

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