Describe the feature or problem you'd like to solve

Every time I launch copilot in interactive mode, I have to press Shift+Tab twice to cycle from Interactive → Plan → Autopilot before I can start working. There's no config key, CLI flag, or environment variable to set the default mode for interactive sessions.

The --autopilot flag only applies to non-interactive -p mode. COPILOT_ALLOW_ALL=true skips the permission prompt but does not change the mode.

Proposed solution

Add a mode config key in ~/.copilot/config.json and/or a --mode CLI flag that sets the default interactive mode on startup.

Config example:

{
  "mode": "autopilot"
}

Flag example:

copilot --mode autopilot

Accepted values: interactive (default), plan, autopilot

This would let users who always work in autopilot skip the manual Shift+Tab cycling on every launch.

Example prompts or workflows

1. copilot --mode autopilot — launches directly into autopilot mode
2. copilot --mode plan — launches directly into plan mode
3. Setting "mode": "autopilot" in ~/.copilot/config.json — every copilot launch defaults to autopilot
4. copilot --mode autopilot --yolo — full autonomous mode, no permission prompts, no mode switching
5. Combined with alias: alias cop='copilot --mode autopilot --yolo' — one command, zero friction

Additional context

• Copilot CLI v0.0.414
• The mode cycle via Shift+Tab works well, but power users who always use autopilot shouldn't need to press it twice on every session start.
• This is similar to how "experimental": true persists in config — mode preference should too.
• The --autopilot flag already exists for -p mode, so extending the concept to interactive mode feels natural.