Decouple projects from rounds with RoundProject join table

Projects now exist at the program level instead of being locked to a
single round. A new RoundProject join table enables many-to-many
relationships with per-round status tracking. Rounds have sortOrder
for configurable progression paths.

- Add RoundProject model, programId on Project, sortOrder on Round
- Migration preserves existing data (roundId -> RoundProject entries)
- Update all routers to query through RoundProject join
- Add assign/remove/advance/reorder round endpoints
- Add Assign, Advance, Remove Projects dialogs on round detail page
- Add round reorder controls (up/down arrows) on rounds list
- Show all rounds on project detail page

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/(mentor)/mentor/projects/page.tsx

@@ -94,16 +94,22 @@ export default function MentorProjectsPage() {
                     <div className="space-y-1">
                       <div className="flex items-center gap-2 text-sm text-muted-foreground">
                         <span>
-                          {project.round.program.year} Edition
+                          {project.program.year} Edition
                         </span>
-                        <span>•</span>
-                        <span>{project.round.name}</span>
+                        {project.roundProjects?.[0]?.round && (
+                          <>
+                            <span>•</span>
+                            <span>{project.roundProjects[0].round.name}</span>
+                          </>
+                        )}
                       </div>
                       <CardTitle className="flex items-center gap-2">
                         {project.title}
-                        <Badge variant={statusColors[project.status] || 'secondary'}>
-                          {project.status.replace('_', ' ')}
-                        </Badge>
+                        {project.roundProjects?.[0]?.status && (
+                          <Badge variant={statusColors[project.roundProjects[0].status] || 'secondary'}>
+                            {project.roundProjects[0].status.replace('_', ' ')}
+                          </Badge>
+                        )}
                       </CardTitle>
                       {project.teamName && (
                         <CardDescription>{project.teamName}</CardDescription>