feat: Default theme on first visit

[theaniketnegi]

Description

I added back the ThemeWatcher component to default to the system theme on first visit to the website.

Proposed Changes

• Adding ThemeWatcher component in src/app/providers.tsx for default theme.

Screenshots

Checklist

Please check the boxes that apply:

• [x] I have rebased my branch on top of the latest main branch.
• [x] I have tested the changes locally
• [x] I ran npm run build and build is successful
• [x] I have added necessary documentation (if applicable)
• [x] I have updated the credits.md file (if applicable)

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