Implement (Contour's) Color Palette Update Notification and report

### Description of the new feature

Implement Dark and Light Mode detection protocol adopted by few terminals and apps (neovim being the most well known i guess)
the specification is presented here: https://github.com/contour-terminal/contour/blob/master/docs/vt-extensions/color-palette-update-notifications.md

### Proposed technical implementation details

_No response_

Start with Contour’s color-palette-update-notifications.md specification linked in the issue, then locate the terminal protocol handling in this repository. Implement the Dark/Light Mode detection and notification/reporting behavior described there, and verify it against the specification.

Written by the indexing model from the issue text.