Ticket IDs, audit log, markdown comments, tabbed detail page

- Tickets get a random display ID (V + 9 digits, e.g. V325813929)
- Ticket detail page has Overview / Comments / Audit Log tabs
- Audit log records every action (create, status, assignee, severity,
  reroute, title/overview edit, comment add/delete) with who and when
- Comments redesigned: avatar (initials + color), markdown rendering
  via react-markdown + remark-gfm, Write/Preview toggle
- Dashboard shows displayId and assignee avatar
- URLs now use displayId (/tickets/V325813929)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/prisma/schema.prisma

@@ -31,9 +31,10 @@ model User {
   createdAt    DateTime @default(now())
   updatedAt    DateTime @updatedAt
 
-  assignedTickets Ticket[]  @relation("AssignedTickets")
-  createdTickets  Ticket[]  @relation("CreatedTickets")
+  assignedTickets Ticket[]   @relation("AssignedTickets")
+  createdTickets  Ticket[]   @relation("CreatedTickets")
   comments        Comment[]
+  auditLogs       AuditLog[]
 }
 
 model Category {
@@ -65,27 +66,29 @@ model Item {
 }
 
 model Ticket {
-  id         String       @id @default(cuid())
-  title      String
-  overview   String
-  severity   Int
-  status     TicketStatus @default(OPEN)
-  categoryId String
-  typeId     String
-  itemId     String
-  assigneeId String?
+  id          String       @id @default(cuid())
+  displayId   String       @unique
+  title       String
+  overview    String
+  severity    Int
+  status      TicketStatus @default(OPEN)
+  categoryId  String
+  typeId      String
+  itemId      String
+  assigneeId  String?
   createdById String
 
   resolvedAt DateTime?
   createdAt  DateTime  @default(now())
   updatedAt  DateTime  @updatedAt
 
-  category  Category @relation(fields: [categoryId], references: [id])
-  type      Type     @relation(fields: [typeId], references: [id])
-  item      Item     @relation(fields: [itemId], references: [id])
-  assignee  User?    @relation("AssignedTickets", fields: [assigneeId], references: [id])
-  createdBy User     @relation("CreatedTickets", fields: [createdById], references: [id])
+  category  Category  @relation(fields: [categoryId], references: [id])
+  type      Type      @relation(fields: [typeId], references: [id])
+  item      Item      @relation(fields: [itemId], references: [id])
+  assignee  User?     @relation("AssignedTickets", fields: [assigneeId], references: [id])
+  createdBy User      @relation("CreatedTickets", fields: [createdById], references: [id])
   comments  Comment[]
+  auditLogs AuditLog[]
 }
 
 model Comment {
@@ -98,3 +101,15 @@ model Comment {
   ticket Ticket @relation(fields: [ticketId], references: [id], onDelete: Cascade)
   author User   @relation(fields: [authorId], references: [id])
 }
+
+model AuditLog {
+  id        String   @id @default(cuid())
+  ticketId  String
+  userId    String
+  action    String
+  detail    String?
+  createdAt DateTime @default(now())
+
+  ticket Ticket @relation(fields: [ticketId], references: [id], onDelete: Cascade)
+  user   User   @relation(fields: [userId], references: [id])
+}