fix(ui): ensure dark mode coherence across charting components

[ArshVermaGit]

Description

This PR resolves an issue where third-party charting libraries (Recharts) used hardcoded hex colors, causing visual clashes when the dashboard was toggled into dark mode. By passing the semantic CSS variables defined in globals.css directly to the charting components, all data visualizations now adapt elegantly to the active theme.

Resolved Issue

Resolves #1551

Key Changes

• PRBreakdownChart.tsx: Updated PR status slices to use semantic variables (var(--accent), var(--success), var(--warning), var(--muted-foreground)).
• ComparisonChart.tsx: Updated the comparison bar graph to use var(--accent-secondary) instead of a hardcoded indigo hex value.
• MiniPRTrendChart.tsx: Swapped hardcoded green/red stroke colors for var(--success) and var(--destructive).
• RepoTimelineChart.tsx: Replaced undefined chart CSS variables with var(--accent-secondary) and var(--warning).
• Audited: Verified that CodingTimeWidget, PRReviewTrendChart, CommitTimeChart, and PRStatusDonutChart already correctly leverage theme tokens.
• Design Decision: Preserved standard GitHub branding colors (e.g., TypeScript blue, JavaScript yellow) to maintain language recognition.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• UI/UX Improvement

How Has This Been Tested?

• Toggled between Light and Dark mode to ensure text, axes, tooltips, and data series contrast properly in both themes.
• Ran npm run build to verify that all modifications compile without type errors.

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[github-actions]

GSSoC Label Checklist 🏷️

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• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

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[ArshVermaGit]

Hi @Priyanshu-byte-coder ! Issue #1551 has been resolved. Please review the PR and merge it under GSSoC. Thanks!

[github-actions]

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