feat(prs): add review time histogram buckets to /api/metrics/prs and …

[Nareshkumawat-star]

Summary

Adds a PR Review Time Distribution Histogram to PRMetrics.tsx and extends /api/metrics/prs/route.ts to return review turnaround time buckets (<1h, 1–4h, 4–24h, 1–3d, 3–7d, 7d+). This replaces reliance on a single average review time with a color-coded distribution chart.

Closes #3245

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Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that changes existing behavior)
• 📝 Documentation update
• ♻️ Refactor / code cleanup (no functional change)
• ⚡ Performance improvement
• 🔒 Security fix
• 🧪 Tests only

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What Changed

• src/app/api/metrics/prs/route.ts:
  • Computed PR review durations and categorized them into 6 standardized time buckets (<1h, 1–4h, 4–24h, 1–3d, 3–7d, 7d+).
  • Added support for single account, GitLab, and combined account aggregation.
• src/components/PRMetrics.tsx:
  • Added Recharts BarChart histogram displaying review time buckets with custom tooltips ("X PRs reviewed within this range").
  • Applied color coding: Emerald (fast), Amber (moderate), Red (slow).

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How to Test

1. Navigate to the DevTrack dashboard and scroll to PR Analytics.
2. Verify that the Review Time Distribution histogram renders below the stat cards and donut chart.
3. Hover over histogram bars to inspect turnaround count tooltips.
4. Toggle time ranges (7d, 30d, 90d) and verify that histogram bucket counts update dynamically.

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Checklist

• Self-reviewed my own diff
• No unnecessary console.log or debug code
• Responsive layout & color legend verified
• Single average skew issue addressed via histogram distribution

[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

[Nareshkumawat-star]

Hi @Priyanshu-byte-coder kindly review and merge it