Add dark theme support to documentation

[Copilot]

Description

Replaced sphinx-rtd-theme with furo to enable dark mode support in the documentation. Furo provides automatic dark mode detection based on system preferences and a manual toggle for users to override.

Changes:

• Replaced sphinx-rtd-theme with furo in doc/requirements.txt
• Updated doc/conf.py to configure Furo with custom brand colors for light and dark modes

Theme Features:

• Automatic dark mode detection based on OS/browser preference
• Manual light/dark/auto toggle in top-right corner
• Modern, clean design with improved readability

Screenshots:

Light mode:

Dark mode:

API reference in dark mode:

Status

• In progress
• Ready for review
• Done

Checklist

• Read the Contributing Guide
• Passes tests
• Linted ( we use pre-commit with ruff )
• Updated documentation

Original prompt

Doc: support dark theme

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
see 2 files with indirect coverage changes

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