feat(teams): add warning for single-member teams

- Show warning on browse page for teams with only 1 member
- Show warning on team detail page for single-member teams
- Helps users understand they need 2+ members to submit

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/hackathon/src/app/teams/browse/page.tsx

@@ -225,6 +225,14 @@ const BrowseTeamsPage: FC = (): ReactElement => {
                     <p className="text-gray-600 dark:text-gray-300 text-sm mb-4 line-clamp-3 font-sans">
                       {team.description}
                     </p>
+                    {(team.member_count || 0) === 1 && !team.has_submission && (
+                      <div className="mb-4 p-2 bg-amber-50 dark:bg-amber-900/20 border border-amber-200 dark:border-amber-800 rounded-lg">
+                        <p className="text-xs text-amber-700 dark:text-amber-400 flex items-center gap-1">
+                          <Icon icon="mdi:alert" className="text-sm shrink-0" />
+                          <span>This team needs at least 2 members to submit</span>
+                        </p>
+                      </div>
+                    )}
                     <div className="space-y-3 mt-auto">
                       {isMyTeam(team.id) ? (
                         <Button