[FEAT] Add Slack/Discord webhook notifications for weekly digest

[RitvikaSavanna]

Summary

Adds Slack/Discord webhook notification support for weekly DevTrack digests.

Users can now configure a webhook URL in profile settings and receive weekly summaries containing commits, merged PRs, and goal completion progress.

Closes #20

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup

Changes Made

• -Added webhook URL input field to profile settings page
• Added webhook_url column to users table in Supabase schema
• Created weekly notifications API route
• Added Slack and Discord webhook payload support
• Added graceful webhook error handling and logging
• Added Vercel cron configuration for weekly scheduling

How to Test

Steps for the reviewer to verify this works:

1. Add a valid Slack or Discord webhook URL in profile settings
2. Run the weekly notifications API route locally
3. Verify webhook message is delivered successfully
4. Test with an invalid webhook URL and confirm errors are logged without crashing
5. Run:
   npm run lint npm run type-check

Screenshots (if UI change)

NA

Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff
• Added/updated tests if applicable

[vercel]

@RitvikaSavanna is attempting to deploy a commit to the PRIYANSHU DOSHI's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

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• level:intermediate — 35 pts
• level:advanced — 55 pts
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Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[github-actions]

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A maintainer will review it within 48 hours. While you wait:

• Make sure CI is passing (type-check + lint)
• Double-check the PR description is filled out and the issue is linked
• Feel free to ask questions in Discussions if you need help

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[Priyanshu-byte-coder]

Merge conflict with main. Rebase to unblock:

git fetch origin && git rebase origin/main
git push --force-with-lease

[Priyanshu-byte-coder]

This PR has merge conflicts with main after recent merges. Please rebase:

git fetch upstream
git rebase upstream/main

Resolve conflicts and force-push.