feat: mentor self-drop dialog on project detail page

DropAssignmentDialog with required reason (10-1000 chars) calls
mentor.dropAssignment, redirects to /mentor on success. Button surfaces
in the project header only when the viewer is the assigned mentor and
the assignment is neither dropped nor completed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/app/(mentor)/mentor/projects/[id]/page.tsx

@@ -2,6 +2,7 @@
 
 import { Suspense, use, useState, useEffect } from 'react'
 import { useRouter } from 'next/navigation'
+import { useSession } from 'next-auth/react'
 import { trpc } from '@/lib/trpc/client'
 import {
   Card,
@@ -31,6 +32,7 @@ import { AnimatedCard } from '@/components/shared/animated-container'
 import { FileViewer } from '@/components/shared/file-viewer'
 import { MentorChat } from '@/components/shared/mentor-chat'
 import { ProjectLogoWithUrl } from '@/components/shared/project-logo-with-url'
+import { DropAssignmentDialog } from '@/components/mentor/drop-assignment-dialog'
 import {
   ArrowLeft,
   AlertCircle,
@@ -76,6 +78,7 @@ const statusColors: Record<string, 'default' | 'secondary' | 'destructive' | 'ou
 
 function ProjectDetailContent({ projectId }: { projectId: string }) {
   const router = useRouter()
+  const { data: session } = useSession()
   const { data: project, isLoading, error } = trpc.mentor.getProjectDetail.useQuery({
     projectId,
   })
@@ -132,8 +135,15 @@ function ProjectDetailContent({ projectId }: { projectId: string }) {
 
   const teamLead = project.teamMembers?.find((m) => m.role === 'LEAD')
   const otherMembers = project.teamMembers?.filter((m) => m.role !== 'LEAD') || []
-  const mentorAssignmentId = project.mentorAssignment?.id
+  const mentorAssignment = project.mentorAssignment
+  const mentorAssignmentId = mentorAssignment?.id
   const programId = project.program?.id
+  const viewerIsAssignedMentor =
+    !!mentorAssignment && session?.user?.id === mentorAssignment.mentor?.id
+  const canDrop =
+    viewerIsAssignedMentor &&
+    !mentorAssignment.droppedAt &&
+    mentorAssignment.completionStatus !== 'completed'
 
   return (
     <div className="space-y-6">
@@ -179,6 +189,12 @@ function ProjectDetailContent({ projectId }: { projectId: string }) {
             )}
           </div>
         </div>
+        {canDrop && mentorAssignmentId && (
+          <DropAssignmentDialog
+            assignmentId={mentorAssignmentId}
+            projectTitle={project.title}
+          />
+        )}
       </div>
 
       {project.assignedAt && (