Add status badge component for group status #73
Description
Create a reusable colored badge that displays group status.
Acceptance Criteria:
- Color mapping: Forming (blue), Active (green), Completed (gray), Paused (yellow), Disputed (red)
- Pill-shaped badge with icon
- Use in GroupCard and group detail page
- Accessible with aria-label
Files: new file src/components/StatusBadge.tsx, src/components/GroupCard.tsx, src/app/groups/[id]/page.tsx