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/mentor.ts

@@ -333,7 +333,7 @@ export const mentorRouter = router({
       // Get projects without mentors
       const projects = await ctx.prisma.project.findMany({
         where: {
-          roundId: input.roundId,
+          roundProjects: { some: { roundId: input.roundId } },
           mentorAssignment: null,
           wantsMentorship: true,
         },
@@ -431,10 +431,17 @@ export const mentorRouter = router({
       include: {
         project: {
           include: {
-            round: {
+            program: { select: { name: true, year: true } },
+            roundProjects: {
               include: {
-                program: { select: { name: true, year: true } },
+                round: {
+                  include: {
+                    program: { select: { name: true, year: true } },
+                  },
+                },
               },
+              orderBy: { addedAt: 'desc' },
+              take: 1,
             },
             teamMembers: {
               include: {
@@ -477,10 +484,17 @@ export const mentorRouter = router({
       const project = await ctx.prisma.project.findUniqueOrThrow({
         where: { id: input.projectId },
         include: {
-          round: {
+          program: { select: { id: true, name: true, year: true } },
+          roundProjects: {
             include: {
-              program: { select: { id: true, name: true, year: true } },
+              round: {
+                include: {
+                  program: { select: { id: true, name: true, year: true } },
+                },
+              },
             },
+            orderBy: { addedAt: 'desc' },
+            take: 1,
           },
           teamMembers: {
             include: {
@@ -528,7 +542,7 @@ export const mentorRouter = router({
     )
     .query(async ({ ctx, input }) => {
       const where = {
-        ...(input.roundId && { project: { roundId: input.roundId } }),
+        ...(input.roundId && { project: { roundProjects: { some: { roundId: input.roundId } } } }),
         ...(input.mentorId && { mentorId: input.mentorId }),
       }
 
@@ -541,9 +555,12 @@ export const mentorRouter = router({
                 id: true,
                 title: true,
                 teamName: true,
-                status: true,
                 oceanIssue: true,
                 competitionCategory: true,
+                roundProjects: {
+                  select: { status: true },
+                  take: 1,
+                },
               },
             },
             mentor: {