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/server/routers/program.ts

@@ -40,7 +40,7 @@ export const programRouter = router({
             orderBy: { createdAt: 'asc' },
             include: {
               _count: {
-                select: { projects: true, assignments: true },
+                select: { roundProjects: true, assignments: true },
               },
             },
           },