Support per-session custom terminal title without disrupting status updates

[devinro]

Describe the feature or problem you'd like to solve

Add a mechanism to set a custom resting-state title per session

Proposed solution

Description:

Currently, the update_terminal_title setting is all-or-nothing. When enabled, the CLI shows helpful status updates (e.g., "Thinking...", current intent) but always resets to "GitHub Copilot" when idle. When disabled, no title updates occur at all.

There's no way to have per-session custom titles while keeping status updates. A global config option wouldn't work because users often have multiple Copilot CLI tabs open, each needing a different title.

Request:

Add a mechanism to set a custom resting-state title per session, such as:

• Command-line flag: copilot --title "🤖 Project X"
• Slash command: /title "🤖 Project X" (or extend /rename to also set terminal title)
• Respect user-set titles: Detect when the user has set a custom title (via escape sequences) and restore that instead of "GitHub Copilot"

Use case:

• I use Windows Terminal with multiple Copilot CLI tabs for different projects
• I want to distinguish tabs with custom titles (e.g., "🐍 Python API", "⚛️ React App")
• I want to see status updates during operations
• When idle, each tab should restore its own custom title, not a global default

Proposed behavior:

• During operations: show status updates as usual
• When idle: restore the session's custom title (if set) or fall back to "GitHub Copilot"

Example prompts or workflows

Example usage:

# Set title at launch
copilot --title "🤖 My Project"

# Or set during session
/title "🤖 My Project"

Additional context

No response