feat(dashboard): add manual "Sync Data" refresh button (#2406)

[Kokila-chandrakar]

Description

Fixes #2406

What was added

• New SyncButton component (src/components/SyncButton.tsx)
  • Uses RefreshCw icon from lucide-react
  • Applies animate-spin Tailwind class during active sync
  • Shows last-synced time in tooltip
• Placed in DashboardHeader top-right alongside existing controls
• Uses router.refresh() (Next.js App Router) to re-fetch server data without a full browser reload

Pillar

• UX Enhancement / Feature

Checklist

• Tested locally
• npm run lint passes
• npm run type-check passes
• Single focused commit

[github-actions]

GSSoC Label Checklist 🏷️

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

Difficulty (pick one):

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

Quality (optional):

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

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

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