Allow to add new entries to the modes dropdown that act as "sticky prompt".

• A mode based on a prompt file: markdown instructions, model and tools.
• Add new "model" field (name or id?)
• 💪 Add new optional "name"/"description" field for a nice displays
• 💪 Support "mode" field in prompt files
• Setting to set default mode
• Mode-flag in prompt files to assign them to the mode picker.
• Golden scenarios based on customer input on how modes differ from prompts
  • Roo Code: Ask, Plan, Act, Debug
  • Levers: Secure vs YOLO, Vibe vs Always Confirm,

Backlog:

• Other idea, new folder/file type: .vscode/modes/automate.mode.md
• New metadata field "alwaysAttach" for must-have context (like plan)
• Later: Automatic mode switching and multi-mode agentic orchestration