feat: add refresh button to each dashboard widget

[Tannuu18]

Summary

Adds per-widget refresh controls to dashboard cards so users can reload individual widgets without refreshing the full page.

Closes #179

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup

Changes Made

• Added a refresh icon button in the header (top-right) for:
  StreakTracker
  ContributionGraph
  PRMetrics
  TopRepos
• Wired each refresh button to re-run only that widget’s data fetch.
• Added loading-state behavior for each button:
• disabled while fetching
• spinner animation during fetch
• aria-label on each refresh button
• Kept existing theme styling for icon state and hover state using muted-foreground and card-foreground token colors.
• Improved ContributionGraph refresh UX so failed refresh does not wipe previously loaded chart data.

How to Test

• Start the app and open the dashboard.
• In each target widget (StreakTracker, ContributionGraph, PRMetrics, TopRepos), click the refresh icon.
• Verify the button disables immediately and icon spins while fetching.
• Verify data refreshes only for that widget (other widgets should remain unchanged).
• Confirm button is in the header row, aligned at top-right near the title.
• Confirm accessibility label exists on each button (Refresh Commit Streaks, Refresh Commit Activity, Refresh PR Analytics, Refresh Top Repositories).
• Trigger a failing refresh scenario for ContributionGraph (for example, temporary API/network failure) and verify prior chart data remains visible with an error message.
• Run npm run lint and npm run type-check.

Screenshots (if UI change)

Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff
• Added/updated tests if applicable

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[Priyanshu-byte-coder]

Good refactor. Extracting fetch into useCallback is the right pattern — lets the button reuse it without duplicating logic. aria-busy, aria-label, disabled-during-load all correct. CSS vars throughout. Covers all 4 widgets (ContributionGraph, PRMetrics, StreakTracker, TopRepos). Approved.

[Priyanshu-byte-coder]

PR is approved but has a conflict with the just-merged #288 (both modify ContributionGraph.tsx). Please rebase on latest main and resolve the conflict — should be straightforward to combine both changes. Then it'll merge automatically.

[Priyanshu-byte-coder]

The refactor to useCallback + async/await and the refresh button look clean — aria-busy, aria-label, disabled state all handled well. However this conflicts with recently merged PRs that touched ContributionGraph.tsx. Please rebase:

git fetch upstream && git rebase upstream/main

Push once rebased — will merge.