feat(pr-insights): add PR Size Distribution analytics visualization

[rastogiradhika]

##Description

Fixes #7798

This PR extends the existing PR Insights dashboard by introducing a PR Size Distribution visualization alongside the Highlights card. It classifies a developer's Pull Requests based on total lines changed (additions + deletions) into three industry-standard complexity buckets.

Changes

1. Backend Data Service (services/github/pr-insights.ts):

• Added PRSizeDistribution interface (atomic, standard, massive).
• Added optional sizeDistribution?: PRSizeDistribution to PRInsightData.
• Aggregated PRs into 3 buckets during single-pass processing:
  • Atomic (<100 LOC)
  • Standard (100–500 LOC)
  • Massive (>500 LOC)

2. New Visualization (components/dashboard/PRInsights/PRSizeDistribution.tsx):

• Built a responsive horizontal bar chart using Recharts (BarChart, Bar, XAxis, YAxis, Tooltip).
• Added full dark mode support and internationalized labels.

3. UI Integration (components/dashboard/PRInsights/PRInsightsClient.tsx):

• Placed PRSizeDistribution into a clean 3-column responsive grid (lg:col-span-2) alongside Highlights (lg:col-span-1).

Notes

1. Reuses existing additions and deletions data already fetched from GitHub GraphQL.
2. Zero additional GitHub API network requests or rate limit overhead.
3. Fully backward compatible with existing API responses and cache entries.

Pillar

• 🎨 Pillar 1 — New Theme Design
• 📐 Pillar 2 — Geometric SVG Improvement
• 🕐 Pillar 3 — Timezone Logic Optimization
• 🛠️ Other (New PR Insights dashboard feature & analytics chart)

Visual Preview

Checklist before requesting a review:

• I have read the CONTRIBUTING.md file.
• I have tested these changes locally (localhost:3000/dashboard/torvalds).
• I have run npm run lint and npm run build locally and resolved all errors.
• My commits follow the Conventional Commits format (feat(pr-insights): ...).
• I have made sure that I have only one commit to merge in this PR.

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[github-actions]

📦 Next.js Bundle Size Report (Gzipped Sizes)

Asset	PR Size	Base Size	Difference	Status
static/chunks/4781-[hash].js	6.90 KB	-	+6.90 KB (++100%)	🆕 New
static/chunks/8427-[hash].js	-	6.81 KB	-6.81 KB (-100.00%)	🗑️ Deleted
static/chunks/8747-[hash].js	-	47.02 KB	-47.02 KB (-100.00%)	🗑️ Deleted
static/chunks/9425-[hash].js	52.20 KB	-	+52.20 KB (++100%)	🆕 New
static/chunks/9453-[hash].js	93.62 KB	93.33 KB	+0.29 KB (+0.31%)	🔴 Regression
static/chunks/app/(root)/dashboard/[username]/page-[hash].js	52.68 KB	52.27 KB	+0.41 KB (+0.78%)	🔴 Regression

📊 Summary of Totals

Category	PR Size	Base Size	Difference
Total JS	3938.06 KB	3917.41 KB	+20.65 KB (+0.53%)
Total CSS	325.89 KB	325.86 KB	+0.03 KB (+0.01%)