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/[teamId]/page.tsx

@@ -491,6 +491,23 @@ const TeamDashboardPage: FC = (): ReactElement => {
               </div>
             )}
 
+            {/* Warning for single member teams */}
+            {members.length === 1 && !team.has_submission && isMember && (
+              <div className="bg-amber-50 dark:bg-amber-900/20 border border-amber-200 dark:border-amber-800 rounded-lg p-4 md:p-6">
+                <div className="flex items-center space-x-3">
+                  <span className="text-3xl">⚠️</span>
+                  <div>
+                    <h3 className="font-bold text-amber-900 dark:text-amber-400">
+                      Team Needs More Members
+                    </h3>
+                    <p className="text-amber-700 dark:text-amber-300 text-sm">
+                      Your team needs at least 2 members to submit a project. Invite someone or wait for join requests!
+                    </p>
+                  </div>
+                </div>
+              </div>
+            )}
+
             {/* Submission Status - Only show to members */}
             {team.has_submission && isMember && (
               <div className="bg-green-50 dark:bg-green-900/20 border border-green-200 dark:border-green-800 rounded-lg p-4 md:p-6">

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