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>

lib/schemas/question-answer.ts

@@ -0,0 +1,10 @@
+import { z } from 'zod'
+
+export const ANSWER_MAX_CHARS = 4000
+
+export const answerQuestionSchema = z.object({
+  questionId: z.string().cuid(),
+  answer: z.string().min(1, 'Antwoord mag niet leeg zijn').max(ANSWER_MAX_CHARS),
+})
+
+export type AnswerQuestionInput = z.infer<typeof answerQuestionSchema>