feat(answer-modal): conform aan dialog-pattern + entity-profile

Story 7 van PBI "Alle dialogen conform docs/patterns/dialog.md".

- lib/schemas/question-answer.ts — gedeeld zod-schema +
  ANSWER_MAX_CHARS constant
- actions/questions.ts gebruikt het gedeelde schema
- AnswerModal: entityDialog* layout-classes, useDirtyCloseGuard,
  useDialogSubmitShortcut, DemoTooltip rond submit + multiple-choice
  knoppen
- docs/specs/dialogs/answer-modal.md — entity-profile

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

actions/questions.ts

@@ -12,15 +12,10 @@
 // realtime updates voor andere clients.
 
 import { revalidatePath } from 'next/cache'
-import { z } from 'zod'
 import { prisma } from '@/lib/prisma'
 import { getSession } from '@/lib/auth'
 import { productAccessFilter } from '@/lib/product-access'
-
-const inputSchema = z.object({
-  questionId: z.string().cuid(),
-  answer: z.string().min(1).max(4000),
-})
+import { answerQuestionSchema } from '@/lib/schemas/question-answer'
 
 type ActionResult = { ok: true } | { ok: false; error: string }
 
@@ -32,7 +27,7 @@ export async function answerQuestion(
   if (!session.userId) return { ok: false, error: 'Niet ingelogd' }
   if (session.isDemo) return { ok: false, error: 'Niet beschikbaar in demo-modus' }
 
-  const parsed = inputSchema.safeParse({ questionId, answer })
+  const parsed = answerQuestionSchema.safeParse({ questionId, answer })
   if (!parsed.success) {
     const first = parsed.error.issues[0]?.message ?? 'Ongeldige invoer'
     return { ok: false, error: first }