feat: implement multi-theme preview canvas (Light, Dark, Dimmed)

[Bhagirath00]

🛠 Pull Request Template

📌 Related Issue

Fixes: #582

🔍 Describe your changes?

I have implemented a Multi-Theme Preview Canvas that allows developers to audit their README designs for accessibility and contrast across all GitHub interface modes.

Key Improvements:

1. Theme Switcher UI: Added a sleek, floating control bar with Sun, Eclipse, and Moon icons anchored to the preview container for one-click toggling.
2. GitHub Simulation: Implemented three scoped modes that perfectly mimic the GitHub experience:

• ☀️ GitHub Light: Pure white background for standard light-mode testing.
• 🌑 GitHub Dimmed: The specialized gray-toned dark mode environment.
• 🌙 GitHub Dark: High-fidelity native black dark mode.

3. Scoped Styling: The theme change is intelligently scoped strictly to the preview canvas. This ensures the tool's main workspace remains in its premium dark aesthetic while only the "README area" acts as a live simulator.
4. Visual Audit Tool: This feature ensures that custom badges, tech icons, and text are 100% readable for every visitor, helping users avoid "invisible" elements on different backgrounds.

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📸 Screenshot

• Theme Switcher

• Github Dark:

• Github Dimmed:

• Github light:

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🧪 Checklist

Please check all that apply:

• I have tested my changes locally.
• I have followed the project's code style and guidelines.
• I have added necessary comments and documentation.
• The code compiles and runs without errors.

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Thank you for contributing!

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[Bhagirath00]

@Mayur-Pagote review it.
Once you confirmed this, plz open this #583

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Project	Deployment	Actions	Updated (UTC)
readme-design-kit	Ready	Preview, Comment	Feb 13, 2026 1:46pm

[Mayur-Pagote]

@Bhagirath00 thank you