feat(dashboard): add interactive Repository Health Explorer (#398)

[Ridanshi]

Summary

• Implements a dedicated /dashboard/repo-health page that surfaces the existing health scoring system (src/lib/repo-health.ts) through interactive visualisations
• Zero changes to the existing health scoring logic — all scoring functions (scoreCommitFrequency, scorePrMergeRate, etc.) are reused directly
• Follows the same routing pattern as /dashboard/career-intelligence (thin server page + rich client component)
• 76 unit tests, all passing; TypeScript strict check clean

Architecture

New lib (src/lib/repo-health-insights.ts)

Pure functions consumed by both the UI and the test suite:

• gradeLetter(score) — A+ → D letter grades
• gradeLabel(grade) — human-readable tier names (Healthy / Needs Attention / At Risk)
• buildRadarData(signals) — normalises each sub-score to 0-100 for the radar chart
• buildBreakdown(signals) — per-dimension earned/max breakdown rows
• generateInsights(signals) — rule-based recommendations engine (5 signal × multi-threshold rules)

New components (src/components/repo-health/)

Component	Purpose
RepoHealthGauge.tsx	SVG semi-circle gauge (no extra dependency)
RepoHealthRadar.tsx	recharts RadarChart — 5 normalised axes
RepoHealthBreakdown.tsx	Weighted score table with progress bars
RepoHealthInsights.tsx	Rule-based recommendations with severity badges
RepoHealthCard.tsx	Compact repo card for the selection panel
RepoHealthExplorer.tsx	Main orchestrator — layout, state, fetch, lazy-loads charts

New page

src/app/dashboard/repo-health/page.tsx — auth-guarded server component

Existing files modified

• src/components/RepoHealthPanel.tsx — added "Full Analysis →" shortcut link to the explorer
• src/app/dashboard/page.tsx — added health explorer entry banner in Analytics & Repositories section

Visualisations

• Gauge: custom SVG arc, no extra dependency, ARIA role="img" label
• Radar chart: recharts RadarChart / Radar, lazy-loaded via next/dynamic
• Score breakdown: 5 rows, each with earned pts / max pts, progress bar, weight %, tooltip with target
• Insights: warnings → infos → successes, colour-coded by severity, metric attribution

Performance

• Recharts components are lazy-loaded (next/dynamic, ssr: false) so the charting bundle is only downloaded when the explorer page is visited
• Days-range preference persisted to localStorage to avoid redundant fetches on re-visits
• Analysis window (7 / 30 / 90 days) passed through to the existing /api/metrics/repo-health endpoint — caching behaviour unchanged
• All expensive computations (buildRadarData, buildBreakdown, generateInsights) wrapped in useMemo
• RepoHealthCard and DetailPanel wrapped in React.memo

Accessibility

• SVG gauge has role="img" and aria-label
• Score breakdown rows use role="progressbar" with aria-valuenow/min/max
• Repo cards use aria-pressed for selection state and descriptive aria-label
• <aside> for the repo list, <main> for the detail panel, <section> for each content block
• Days selector has a visible <label> (via sr-only) and aria-label
• "Back to Dashboard" link with aria-label

Test results

Test Files  1 passed (1)
      Tests  76 passed (76)

Regression tests verify all 5 existing scoring functions remain unchanged. New tests cover gradeLetter, gradeLabel, buildRadarData, buildBreakdown, and generateInsights at all significant thresholds.

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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 conflicts with main. Please rebase:

git fetch origin && git rebase origin/main

Then push and we'll review.

[Priyanshu-byte-coder]

This PR has merge conflicts with main. Please rebase to continue:

git fetch origin
git rebase origin/main

[Ridanshi]

Hi, I've pushed the requested fixes, resolved conflicts, and all completed checks are passing. The Playwright smoke test is still in progress. Could someone please review when convenient? Thanks!