feat: add activity ring chart with 24-segment SVG arc visualization

[devendra-w]

Summary

Adds a circular 24-segment activity ring chart that visualizes commit frequency by hour of day, replacing the previous 4-block radar chart approach.

Closes #228

Type of Change

• New feature

Changes Made

• Added src/app/api/metrics/contributions/hourly/route.ts — new endpoint that fetches commits and groups them by local hour (0–23)
• Rewrote src/components/ActivityRingChart.tsx — custom SVG arc chart with 24 segments, hover tooltips, peak hour highlight, and mount animation that respects prefers-reduced-motion

How to Test

1. Sign in and navigate to /dashboard
2. Scroll to the Activity Ring section
3. Verify 24 segments render in a clock-like layout with labels at 12am, 6am, 12pm, 6pm
4. Hover over any segment — center should update to show that hour and commit count
5. The most active hour segment should be highlighted
6. Switch between Last 7d / 30d / 90d — chart should update accordingly

Screenshots (if UI change)

Checklist

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

[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

[devendra-w]

@Priyanshu-byte-coder PR is ready for the check and can be cleanly merged. Please do add a difficulty label to this issue. Thankyou!

[Priyanshu-byte-coder]

Good feature — four fixes before merge:

1. Missing EOF newlines on three new files:

   • src/app/api/metrics/contributions/daily/route.ts
   • src/app/api/metrics/contributions/hourly/route.ts
   • src/components/ActivityRingChart.tsx

2. Hardcoded color — ActivityRingChart.tsx error state uses text-red-400. Replace with text-[var(--destructive)].

3. withMetricsCache not used on new API routes — all other metric routes cache responses. Add caching to /hourly and /daily consistent with the rest of the codebase.

4. Server timezone — date.getHours() on the server gives UTC hours, not user's local hours. Worth a code comment so future contributors don't assume it's timezone-aware.

[devendra-w]

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

• Added EOF newlines to all three new files
• Replaced text-red-400 with text-[var(--destructive)]
• Added withMetricsCache caching to both /hourly and /daily routes
• Added timezone comment to clarify date.getHours() returns UTC on the server

Regarding the E2E / Playwright smoke tests failure it appears to be a JWT_SESSION_ERROR decryption issue in the CI environment and is unrelated to this PR's changes. All 7 other checks are passing including Build, Lint, Type check, and Dependency audit.
Ready for re-review!