feat: Add PR open time distribution histogram [issue: #167]Feat/pr open time histogram

[abdullahxyz85]

Summary [Issue: #167 ]

Adds a histogram showing how long PRs stay open before being merged, broken into time buckets to reveal code review velocity patterns.

What's Changed

• New horizontal bar chart in PRMetrics component showing PR open time distribution
• 4 time buckets: < 1h, 1-24h, 1-7d, > 7d
• Uses recharts BarChart with responsive sizing
• Interactive tooltips showing exact PR count per bucket
• Respects existing 30-day range filter (ready for future range selection)
• All styling uses CSS variables for theme consistency

Implementation Details

• Modified /api/metrics/prs/route.ts to calculate and return time distribution data
• Updated PRMetrics.tsx to render histogram below existing stats
• Added TypeScript interfaces for proper type safety
• Maintains backward compatibility with existing metrics

Visual Preview

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Acceptance Criteria Met [issue: #167 ]

• ✅ New chart in PR Analytics widget
• ✅ 4 time buckets with intuitive labels
• ✅ Horizontal bar chart using recharts
• ✅ Data from existing /api/metrics/prs endpoint
• ✅ Respects 30-day range
• ✅ Uses CSS variables for colors
• ✅ Tooltip shows exact count on hover

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[abdullahxyz85]

@Priyanshu-byte-coder check it now, I close the older PR and create new PRs by spliting from each others, please review and merge and make sure to add the labels, gssoc:approved and level.

[Priyanshu-byte-coder]

Three bugs in prs/route.ts:

1. Duplicate fetchPRMetrics function definition
The diff adds a second async function fetchPRMetrics(token, days) above the original async function fetchPRMetrics(token) that still exists in the file. TypeScript will throw a duplicate identifier error. Remove the old fetchPRMetrics signature and replace it with the new days parameter version. This is a merge conflict artifact.

2. Duplicate mergeRate in return object

return {
  ...
  mergeRate: data.total_count > 0 ? merged / data.total_count : 0,  // ← first (wrong)
  timeDistribution,
  mergeRate: sampleTotal > 0 ? merged / sampleTotal : 0,            // ← duplicate
};

Duplicate property — remove the first mergeRate line. The sampleTotal formula is correct.

3. Time distribution uses closedPRs + closed_at — should use mergedPRs + merged_at
The buckets loop over closedPRs (PRs closed without merging) and use closed_at. This mixes rejected PRs into the 'time to open' distribution. The chart should show time-to-merge only — loop over mergedPRs and use merged_at.

[abdullahxyz85]

@Priyanshu-byte-coder Done! Please make sure to add the label: gssoc:approved and level:adavanced.

[Priyanshu-byte-coder]

1. route.ts will not compile — unresolved merge conflict artifacts: duplicate formatPRMetrics declarations, two result bindings in same scope, unclosed if block. Fully rebase on main and resubmit. 2. Cache bypassed — fetchPRMetrics called directly in all branches, skipping fetchCachedPRMetrics. Restore caching. 3. cursor={{ fill: var(--accent)/10 }} — invalid Recharts prop value. Use rgba() instead.

[abdullahxyz85]

@Priyanshu-byte-coder Conflicts are resolved and fix all the things , please review and merge it and add label: gssoc:approved and level