feat: add coding time by hour heatmap widget(most productive hours)

[MaitrayeeK]

Summary

Adds a new Most Productive Hours widget to the dashboard — a 24×7 heatmap
grid showing commit density by hour of day and day of week

Closes #1064

Type of Change

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

Changes Made

• src/app/api/metrics/productive-hours/route.ts — New API route. Fetches GitHub PushEvents for the last 90 days, groups commits by (dayOfWeek, hour) using the user's local timezone (passed as tz query param), and returns a flat 7×24 grid of { day, hour, avg } objects plus a peak cell.
• src/components/ProductiveHoursWidget.tsx — New widget. Renders the grid with color-intensity cells, hover tooltip, 🔥 peak label, legend, and info tooltip on the title.
• src/app/dashboard/page.tsx — Imports and places the new widget.

Screenshots (if UI change)

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

Accessibility Checklist

• Proper keyboard navigation tested
• Responsive UI verified
• Accessibility labels added where needed

[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]

This PR has merge conflicts with main. Please rebase your branch against the latest main and force-push to resolve. Run: git fetch upstream && git rebase upstream/main

[MaitrayeeK]

Conflict resolved. Please review and merge when you get a chance. Thanks!

The UI has changed slightly due to the recent updates. Attaching a screenshot for reference.

[Priyanshu-byte-coder]

This PR has developed merge conflicts after recent merges to main. Please rebase onto the latest main branch, resolve all conflicts, and force-push. Once the PR is conflict-free it will be reviewed for merging.

[MaitrayeeK]

Conflict resolved. Please review and merge. Thanks!