feat(ST-bsjoqjnr): UserQuestion model + PLAN_CHAT enum-waarde

- Voeg PLAN_CHAT toe aan ClaudeJobKind enum
- Voeg UserQuestionStatus enum toe (pending, answered)
- Voeg UserQuestion model toe met idea_id, user_id, question, answer, status
- Koppel user_questions relatie aan Idea model
- Migratie: 20260505120000_add_user_question_plan_chat

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

prisma/schema.prisma

@@ -90,6 +90,7 @@ enum ClaudeJobKind {
   TASK_IMPLEMENTATION
   IDEA_GRILL
   IDEA_MAKE_PLAN
+  PLAN_CHAT
 }
 
 enum IdeaLogType {
@@ -101,6 +102,11 @@ enum IdeaLogType {
   JOB_EVENT
 }
 
+enum UserQuestionStatus {
+  pending
+  answered
+}
+
 model User {
   id                 String           @id @default(cuid())
   username           String           @unique
@@ -409,9 +415,10 @@ model Idea {
   created_at  DateTime   @default(now())
   updated_at  DateTime   @updatedAt
 
-  questions ClaudeQuestion[]
-  jobs      ClaudeJob[]
-  logs      IdeaLog[]
+  questions      ClaudeQuestion[]
+  jobs           ClaudeJob[]
+  logs           IdeaLog[]
+  user_questions UserQuestion[]
 
   @@unique([user_id, code])
   @@index([user_id, archived, status])
@@ -432,6 +439,23 @@ model IdeaLog {
   @@map("idea_logs")
 }
 
+model UserQuestion {
+  id         String             @id @default(cuid())
+  idea_id    String
+  user_id    String
+  question   String             @db.Text
+  answer     String?            @db.Text
+  status     UserQuestionStatus @default(pending)
+  created_at DateTime           @default(now())
+  updated_at DateTime           @updatedAt
+
+  idea       Idea               @relation(fields: [idea_id], references: [id], onDelete: Cascade)
+
+  @@index([idea_id, status])
+  @@index([user_id])
+  @@map("user_questions")
+}
+
 model LoginPairing {
   id                 String    @id @default(cuid())
   secret_hash        String