feat(tui): implement double Ctrl+C to quit

[shoaibansari5398]

What does this PR do?

Fixes #9041 Implements a "double Ctrl+C to quit" mechanism to prevent accidental session termination.

How did you verify your code works?

Changes

• Modified packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx.
• Added quitArmed state to the Prompt component.
• Updated app_exit keybinding handler:
  • First Press (on empty prompt): Shows a toast "Press Ctrl+C again to exit" and sets a 3-second timeout.
  • Second Press (within 3s): Exits the application.

Testing

• Verified manually:
  • Pressing Ctrl+C once on empty prompt shows the toast.
  • Pressing again within 3s exits.
  • Pressing again after 3s shows the toast again (timeout reset).
  • Ctrl+C with text still clears the input (existing behavior).