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>

prisma/schema.prisma

@@ -335,6 +335,7 @@ model Program {
 
   // Relations
   rounds            Round[]
+  projects          Project[]
   learningResources LearningResource[]
   partners          Partner[]
   applicationForms  ApplicationForm[]
@@ -351,6 +352,7 @@ model Round {
   slug            String?     @unique // URL-friendly identifier for public submissions
   status          RoundStatus @default(DRAFT)
   roundType       RoundType   @default(EVALUATION)
+  sortOrder       Int         @default(0)  // Progression order within program
 
   // Submission window (for applicant portal)
   submissionDeadline DateTime? // Deadline for project submissions
@@ -375,7 +377,7 @@ model Round {
 
   // Relations
   program          Program          @relation(fields: [programId], references: [id], onDelete: Cascade)
-  projects         Project[]
+  roundProjects    RoundProject[]
   assignments      Assignment[]
   evaluationForms  EvaluationForm[]
   gracePeriods     GracePeriod[]
@@ -419,13 +421,12 @@ model EvaluationForm {
 
 model Project {
   id              String           @id @default(cuid())
-  roundId         String
+  programId       String
 
   // Core fields
   title           String
   teamName        String?
   description     String?          @db.Text
-  status          ProjectStatus    @default(SUBMITTED)
 
   // Competition category
   competitionCategory CompetitionCategory?
@@ -474,7 +475,8 @@ model Project {
   updatedAt DateTime @updatedAt
 
   // Relations
-  round            Round              @relation(fields: [roundId], references: [id], onDelete: Cascade)
+  program          Program            @relation(fields: [programId], references: [id], onDelete: Cascade)
+  roundProjects    RoundProject[]
   files            ProjectFile[]
   assignments      Assignment[]
   submittedBy      User?              @relation("ProjectSubmittedBy", fields: [submittedByUserId], references: [id], onDelete: SetNull)
@@ -485,8 +487,7 @@ model Project {
   awardVotes         AwardVote[]
   wonAwards          SpecialAward[]   @relation("AwardWinner")
 
-  @@index([roundId])
-  @@index([status])
+  @@index([programId])
   @@index([tags])
   @@index([submissionSource])
   @@index([submittedByUserId])
@@ -495,6 +496,23 @@ model Project {
   @@index([country])
 }
 
+model RoundProject {
+  id         String        @id @default(cuid())
+  roundId    String
+  projectId  String
+  status     ProjectStatus @default(SUBMITTED)
+  addedAt    DateTime      @default(now())
+
+  // Relations
+  round      Round         @relation(fields: [roundId], references: [id], onDelete: Cascade)
+  project    Project       @relation(fields: [projectId], references: [id], onDelete: Cascade)
+
+  @@unique([roundId, projectId])
+  @@index([roundId])
+  @@index([projectId])
+  @@index([status])
+}
+
 model ProjectFile {
   id        String   @id @default(cuid())
   projectId String