Fix JSX attribute syntax in constraint editor descriptions

German curly quotes („…") combined with a closing straight " inside
JSX attribute values were terminating the attribute prematurely, e.g.
`description="Beispiel: „X" (jugendgerecht)."` lost everything after
the inner straight quote. Switch all such descriptions to the JSX
expression form `description={"…"}` so the inner quotes are part of
a JavaScript string literal and parsed correctly.

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

studio-v2/app/stundenplan/_components/regeln/TeacherUnavailableWindowEditor.tsx

@@ -28,7 +28,7 @@ export function TeacherUnavailableWindowEditor() {
     <ConstraintShell
       testId="teacher-unavailable-window-editor"
       title="Lehrer: Zeitfenster nicht verfuegbar"
-      description="Beispiel: „Lehrer Z Dienstags 13:00–17:00 nicht"."
+      description={"Beispiel: „Lehrer Z Dienstags 13:00–17:00 nicht"."}
       newLabel="+ Neue Regel"
       newDisabled={teachers.length === 0}
       prereqWarning={teachers.length === 0 ? 'Zuerst Lehrer anlegen.' : null}