Add round delete with confirmation dialog

- Add delete procedure to round tRPC router with cascade and audit log
- Add delete option to rounds list dropdown menu
- Show confirmation dialog with project/assignment counts before deletion

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

src/server/routers/round.ts

@@ -341,6 +341,45 @@ export const roundRouter = router({
       })
     }),
 
+  /**
+   * Delete a round (admin only)
+   * Cascades to projects, assignments, evaluations, etc.
+   */
+  delete: adminProcedure
+    .input(z.object({ id: z.string() }))
+    .mutation(async ({ ctx, input }) => {
+      const round = await ctx.prisma.round.findUniqueOrThrow({
+        where: { id: input.id },
+        include: {
+          _count: { select: { projects: true, assignments: true } },
+        },
+      })
+
+      await ctx.prisma.round.delete({
+        where: { id: input.id },
+      })
+
+      // Audit log
+      await ctx.prisma.auditLog.create({
+        data: {
+          userId: ctx.user.id,
+          action: 'DELETE',
+          entityType: 'Round',
+          entityId: input.id,
+          detailsJson: {
+            name: round.name,
+            status: round.status,
+            projectsDeleted: round._count.projects,
+            assignmentsDeleted: round._count.assignments,
+          },
+          ipAddress: ctx.ip,
+          userAgent: ctx.userAgent,
+        },
+      })
+
+      return round
+    }),
+
   /**
    * Check if a round has any submitted evaluations
    */