Add a dark-mode theme toggle and persist preference

[Gupta-02]

Description: Implement a site-level theme toggle (light/dark) stored in localStorage and used by Docusaurus theme to persist user preference.
Why it matters: Improves UX and engagement.
Acceptance criteria:
Add a visible toggle in the header (or theme controls) that toggles dark/light
Preference persists across reloads via localStorage
Works in both desktop and mobile view
Labels: enhancement, frontend
Difficulty: hard
Files/areas: src/theme/, src/components/

[github-actions]

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[sanjay-kv]

we already have this @Gupta-02

[Gupta-02]

So should i close this or work upon it sir

[sanjay-kv]

i will close this

[github-actions]

✅ This issue has been closed. Thank you for your contribution!