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/(admin)/admin/projects/new/page.tsx

@@ -73,6 +73,7 @@ function NewProjectPageContent() {
   const rounds = programs?.flatMap((p) =>
     (p.rounds || []).map((r) => ({
       ...r,
+      programId: p.id,
       programName: `${p.year} Edition`,
     }))
   ) || []
@@ -117,6 +118,7 @@ function NewProjectPageContent() {
     })
 
     createProject.mutate({
+      programId: selectedRound!.programId,
       roundId: selectedRoundId,
       title: title.trim(),
       teamName: teamName.trim() || undefined,