feat: implement persistent unread notification badge with realtime count

[Nagajyothi-tammisetti]

Related Issue

Closes #134

Changes Made

Backend

• Added isRead and readAt fields to notifications
• Added unread count endpoint
• Added mark-all-read endpoint
• Added realtime unread count socket event

Frontend

• Added unread badge on notification bell
• Persisted count across refreshes
• Added realtime badge updates
• Reset count when notifications are viewed

Testing

• Verified unread count persistence
• Verified realtime updates through WebSocket
• Verified mark-all-read functionality
• Verified badge reset behavior

[vercel]

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[github-actions]

❌ PR Validation Failed

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• Non-empty Description section
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Please edit your PR description to include them, then push a new commit or re-save the description. 📝

[github-actions]

⚠️ DCO Sign-off Missing

The following commit(s) are missing a Signed-off-by: line:

• 308119f — feat: add persistent unread notification badge

How to fix:

# For the last commit:
git commit --amend --signoff
git push --force-with-lease

# For multiple commits (replace N with the count):
git rebase HEAD~1 --signoff
git push --force-with-lease

By signing off, you certify that you have the right to submit this contribution under the project's license. See DCO. ✍️

[github-actions]

⚠️ @Nagajyothi-tammisetti — your PR body doesn't declare a program (GSSoC/NSoC/General). Please update your description to include the program name. 📝

[github-actions]

ℹ️ No mentor:* label was found on this PR at merge time. The fallback label mentor:Ayushh-Sharmaa has been applied automatically. If this is incorrect, a maintainer can update it. 🏷️