feat: implement dark mode toggle #342

[SinghSwayam]

Description

This PR implements a full system-wide Dark Mode for the application (Issue #342). It introduces a ThemeContext for centralized theme management and ensures the app automatically respects the user's system preference on first load.

Key Changes:

• Theme Context: Created src/Context/ThemeContext.js to manage light/dark state and provide colors to components.
• Animated Toggle: Integrated @theme-toggles/react (specifically the Expand animation) for a polished UX.
• System Preference: The app now detects and applies the user's OS color scheme (Light/Dark) by default.
• Component Updates: Updated Header, Timeline, App, and other components to consume dynamic colors from the new context.

Dependencies Added:

• @theme-toggles/react (^4.1.0)

Fixes #342

Type of Change:

• Code
• User Interface

Code/Quality Assurance Only

• New feature

How Has This Been Tested?

I have performed manual testing to verify the following scenarios:

1. Toggle Functionality: Verified that clicking the sun/moon icon successfully toggles the theme.
2. System Default: Verified that the app correctly loads in Dark Mode if the OS system preference is set to Dark Mode.
3. Visual Consistency: Checked all text, backgrounds, and cards (Projects, Timeline, Events) to ensure appropriate contrast and visibility in both modes.

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Checklist:

• My PR follows the style guidelines of this project
• I have performed a self-review of my own code or materials
• I have commented my code or provided relevant documentation, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have attached link of deployed site : https://anitab-org-github-io.vercel.app/
• Any dependent changes have been merged

Code/Quality Assurance Only

• My changes generate no new warnings
• My PR currently breaks something (fix or feature that would cause existing functionality to not work as expected)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been published in downstream modules