actions: promoteTodoToIdeaAction (M12 T-499)

actions/todos.ts:
- promoteTodoToIdeaAction(todoId): auth + demo + scope + already-archived
  guards. Atomic \$transaction creates DRAFT Idea (with auto IDEA-NNN code)
  and archives source Todo + IdeaLog{NOTE}.
- Anders dan Todo→PBI/Story (die de todo deleten): we ARCHIVEREN. De idea
  wordt het nieuwe planningsartifact; de archived todo bewaart het
  vertrekpunt (zie M12 grill-keuze 12).

Tests: 5 cases — happy, auth-401, demo-403, scope-404, already-archived-422.

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

actions/todos.ts

@@ -241,6 +241,60 @@ export async function promoteTodoToStoryAction(_prevState: unknown, formData: Fo
   return { success: true }
 }
 
+// M12: promote a Todo into a DRAFT Idea. Anders dan Todo→PBI/Story (die de
+// todo deleteert) ARCHIVEREN we de todo hier — het idee houdt zelf de
+// planningsgeschiedenis bij, en de archived todo bewaart het oorspronkelijke
+// vertrekpunt.
+export async function promoteTodoToIdeaAction(todoId: string): Promise<
+  { success: true; idea_id: string; idea_code: string } | { error: string; code?: number }
+> {
+  const session = await getSession()
+  if (!session.userId) return { error: 'Niet ingelogd', code: 401 }
+  if (session.isDemo) return { error: 'Niet beschikbaar in demo-modus', code: 403 }
+
+  if (!todoId) return { error: 'todoId is verplicht', code: 422 }
+
+  const todo = await prisma.todo.findFirst({
+    where: { id: todoId, user_id: session.userId },
+    select: { id: true, title: true, description: true, product_id: true, archived: true },
+  })
+  if (!todo) return { error: 'Todo niet gevonden', code: 404 }
+  if (todo.archived) return { error: 'Todo is al gearchiveerd', code: 422 }
+
+  const userId = session.userId
+  // Lazy-import om dit server-only bestand niet te dwingen in een client bundle.
+  const { nextIdeaCode } = await import('@/lib/idea-code-server')
+
+  const idea = await prisma.$transaction(async (tx) => {
+    const code = await nextIdeaCode(userId, tx)
+    const created = await tx.idea.create({
+      data: {
+        user_id: userId,
+        product_id: todo.product_id,
+        code,
+        title: todo.title,
+        description: todo.description ?? null,
+        status: 'DRAFT',
+      },
+      select: { id: true, code: true },
+    })
+    await tx.todo.update({ where: { id: todoId }, data: { archived: true } })
+    await tx.ideaLog.create({
+      data: {
+        idea_id: created.id,
+        type: 'NOTE',
+        content: `Promoted from Todo ${todoId}`,
+        metadata: { source_todo_id: todoId },
+      },
+    })
+    return created
+  })
+
+  revalidatePath('/ideas')
+  revalidatePath('/todos')
+  return { success: true, idea_id: idea.id, idea_code: idea.code }
+}
+
 export async function updateRolesAction(roles: string[]) {
   const session = await getSession()
   if (!session.userId) return { error: 'Niet ingelogd' }