fix(metrics): include timezone in cache keys for timezone-sensitive endpoints

[0xPyxis]

Summary

Fixes a timezone-related caching bug in metrics endpoints.

Closes #2716

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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

• Added timezone to the cache key parameters in src/app/api/metrics/contributions/route.ts
• Added timeZone to the cache key parameters in src/app/api/metrics/streak/route.ts
• Added timeZone to the cache key parameters in src/app/api/metrics/consistency-score/route.ts
• Scoped the consistency score cache by timezone to prevent stale cross-timezone cache hits

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How to Test

1. Set the dashboard timezone to one timezone (e.g. Asia/Kolkata) and load Contributions, Streak, or Consistency Score metrics.
2. Change the timezone preference to another timezone (e.g. America/New_York).
3. Reload the metrics endpoints.

Expected result:

Metrics should be recalculated or fetched from a timezone-specific cache entry instead of reusing data generated for a different timezone.

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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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Additional Context

The cache keys previously omitted timezone information, causing timezone-sensitive metrics to be reused across different timezone settings. This change ensures cache entries are properly scoped per timezone.

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[github-actions]

GSSoC Label Checklist 🏷️

@Umbrella-io — 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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[Legit-Ox]

Please add a WHY comment here.

[Priyanshu-byte-coder]

Good catch on the timezone cache key bug — this is a legitimate fix. Two things before merge:

1. Indentation bug in consistency-score/route.ts — the replacement line has zero indentation instead of the original 2-space indent:

   -  const key = `metrics:${cacheContext.userId}:consistency-score:${cacheContext.accountKey}`;
   +const key = `metrics:${cacheContext.userId}:consistency-score:${cacheContext.accountKey}:${timeZone}`;

   Should be 2-space indented to match the surrounding code.

2. Labels — please remove type:feature and type:performance labels. This is a pure bug fix.

Fix the indentation and this is good to go.