style(landing): enhance text contrast and readability across hero and feature sections

[mahavirb22]

Summary

Resolves severe low-contrast text issues on the landing page that violated WCAG AA accessibility standards. Upgraded the primary stat counters, sub-labels, and feature walkthrough descriptions to readable, high-contrast Tailwind slate/gray utility shades.

Closes #1497

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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

• Upgraded the 4 primary numerical stat counters (847+, 43+, etc.) from faint greys to high-contrast bold shades in src/app/page.tsx / landing components.
• Darkened the descriptive body copy beneath STREAK TRACKING, PR ANALYTICS, and WEEKLY GOALS to ensure legibility against the light card containers.

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How to Test

1. Spin up the app locally (pnpm dev).
2. Navigate to http://localhost:3000.
3. Observe the hero statistics numbers and the feature section cards.
4. Verify all text is easily legible without straining the eyes.

Expected result: Crisp, accessible text hierarchy across the entire landing page viewport.

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Checklist

• Linked the related issue above
• Self-reviewed my own diff
• No unnecessary console.log, debug code, or commented-out blocks
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Added or updated tests where applicable
• Updated documentation / comments if behavior changed

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Accessibility (UI changes only)

• Keyboard navigation works correctly
• Color contrast meets WCAG AA standard
• ARIA labels / roles added where needed
• Tested on mobile / responsive layout

[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

[mahavirb22]

Hi! My PR is consistently failing the Playwright workflows with:

ERR_PNPM_LOCKFILE_CONFIG_MISMATCH

I checked my branch against the latest upstream/main, and both package.json and pnpm-lock.yaml match exactly. I also verified that upstream/main itself has an inconsistency: pnpm-lock.yaml contains a postcss override that isn't present in package.json.

Since my PR only changes landing page text contrast and doesn't touch dependencies, it looks like this may be a repository/workflow issue rather than something introduced by my branch. Could you please take a look?