feat: add contribution heatmap drill-down sheet on cell click (#227)

[devendra-w]

Summary

Adds a slide-in panel when clicking a heatmap cell, showing the daily commit breakdown by repository. Panel is keyboard accessible and closes on Escape or backdrop click.
Closes #227

Type of Change

• New feature

Changes Made

• Added src/components/DailyBreakdownSheet.tsx — slide-in panel showing date, repo names, commit counts and links
• Updated src/components/ContributionHeatmap.tsx — added selectedDate state and onClick handler on each cell
• Panel closes on Escape key or backdrop click
• Loading skeleton shown while fetching data

How to Test

1. Sign in and navigate to /dashboard
2. Click any heatmap cell
3. Verify slide-in panel appears from the right showing the date
4. Press Escape or click backdrop to close
5. Verify future date cells are not clickable

Screenshots (if UI change)

N/A - requires auth to test

Checklist

• Linked issue in summary
• npm run lint passes locally
• Self-reviewed the diff
• Added/updated tests if applicable

[vercel]

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

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[github-actions]

GSSoC Label Checklist 🏷️

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

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[Priyanshu-byte-coder]

Feature is broken — API shape mismatch.

The component fetches /api/metrics/contributions?days=365 and reads result.repos?.[date]. The actual API response shape is { days, total, data: Record<string, number> } — a flat date→count map with no repos key. result.repos will always be undefined, so the sheet always shows "No commit data available for this day."

To fix: either add a new endpoint that returns per-repo breakdown for a specific date, or restructure the existing endpoint to include repo-level data.

Other issues:

• Full 365-day dataset is re-fetched on every cell click — the heatmap already has this data, pass it down as a prop instead
• Missing EOF newline on both DailyBreakdownSheet.tsx and ContributionHeatmap.tsx
• onClose in useEffect dep array with an inline () => setSelectedDate(null) creates a new ref each render, causing the event listener to be removed/re-added constantly — wrap in useCallback or use a useRef

[devendra-w]

Hi @Priyanshu-byte-coder! I've addressed all the requested changes:

• Fixed the API shape mismatch by creating a new /api/metrics/contributions/daily endpoint that returns per-repo breakdown for a specific date
• Eliminated the redundant 365-day re-fetch on every cell click by passing heatmapData as a prop
• Fixed the useEffect event listener being removed/re-added constantly using useRef
• Added EOF newlines to both files

Ready for re-review!

[Priyanshu-byte-coder]

Issues found in this PR:

• Missing EOF newline — add a trailing newline to all modified files.