test(streak): add unit tests for commit streak calculator edge cases

[Nareshkumawat-star]

Summary

Adds comprehensive unit test coverage for the commit streak calculation engine (src/lib/streak.ts). This ensures streak counts remain accurate across critical edge cases like day boundaries, timezone differences, streak freeze tokens, intraday deduplication, and active grace periods.
Closes #3251

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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 cleamprovement
• 🔒 Security fix
• 🧪 Tests only

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What Changed

• Created src/lib/__tests__/streak.test.ts to test edge cases:
  • 5 consecutive days calculation (streak = 5).
  • Streak freeze token bridging 1-day gap.
  • Streak broken when gap exceeds available freeze tokens.
  • Midnight boundary commits (23:59 vs 00:01 on adjacent days).
  • Timezone-aware date bucketing (UTC vs IST).
  • Intraday commit deduplication (multiple commits on same day = 1 streak day).
  • Grace period validation (committed yesterday, no commit today yet).

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How to Test

1. Run the Vitest test runner for the streak test file:

   npx vitest run src/lib/__tests__/streak.test.ts

Expected result: All unit tests for streak calculation pass cleanly.

Checklist
Linked the related issue above
Self-reviewed my own diff
No unnecessary console.log, debug code, or commented-out blocks
Added or updated tests where applicable
Additional Context
Branch: test/commit-streak-unit-tests
Direct PR creation link: https://github.com/Nareshkumawat-star/devtrack/pull/new/test/commit-streak-unit-tests
1:41 PM

[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

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• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

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Points formula: (difficulty × quality_multiplier) + type_bonus

[Nareshkumawat-star]

Hi @Priyanshu-byte-coder kindly review and merge it