fix: add timeBlocks aggregation to contributions endpoint for CommitTimeChart

[ionfwsrijan]

Description

Fixes #1309

The CommitTimeChart component reads the timeBlocks field from the /api/metrics/contributions response to display commit distribution across morning, afternoon, evening, and night. However, the backend endpoint never computed or returned this field, causing the chart to always render "No commits" for every user.

Changes

src/app/api/metrics/contributions/route.ts

• Added TimeBlocks interface with morning, afternoon, evening, night counters
• Added timeBlocks field to ContributionResponse
• Computes time-of-day bins inside fetchContributionsForAccount by extracting the hour from each commit's author.date:
  • Morning (6–12): timeBlocks.morning++
  • Afternoon (12–18): timeBlocks.afternoon++
  • Evening (18–22): timeBlocks.evening++
  • Night (22–6): timeBlocks.night++
• Returns timeBlocks alongside existing days, total, data, and commits
• Merges timeBlocks correctly in the combined-accounts path (per-block sums)
• Passes through timeBlocks from the GitHub result in GitLab merge
• GitLab contributions return zeroed timeBlocks (events don't carry hour precision)

Verification

1. Navigate to /dashboard and observe the "Commits by Time of Day" chart
2. Before: always shows "No commits in the last N days"
3. After: shows horizontal bar chart with commit counts for each time block, plus peak-time label
4. Test with 7d / 30d / 90d range selector
5. Verify combined-accounts mode correctly aggregates time blocks across all linked accounts

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[github-actions]

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[ionfwsrijan]

@Priyanshu-byte-coder You may review and merge this

[github-actions]

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