fix(dashboard): fetch real commit activity from weekly-summary API instead of hardcoded data

[nyxsky404]

Summary

Replaced the hardcoded MOCK_TELEMETRY_DATA array in CommitActivityWidget with a useEffect fetch to /api/metrics/weekly-summary, which already returns real per-day commit counts (dailyCommits) for the authenticated user.

Changes

• Removed MOCK_TELEMETRY_DATA constant.
• Added useEffect to fetch /api/metrics/weekly-summary and map the dailyCommits response into the chart data format.
• Added proper loading, error, and empty states so the widget never silently falls back to fake numbers.
• Line additions/deletions display as 0 since the weekly-summary endpoint does not return per-day diff stats; this is honest rather than fabricated.

Fixes #3351

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[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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• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

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Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[nyxsky404]

@Priyanshu-byte-coder Please review, repo is already stared by me