feat: edit and delete pairs in GenerateIt

- Backend: PATCH /api/directus/db-pairs/<id> updates level, statement, question
  (creates question if new, removes if cleared)
- Backend: DELETE /api/directus/db-pairs/<id> removes pair + all junctions,
  questions and statements
- Frontend: inline edit form per pair (level slider, statement, question)
- Frontend: delete button per pair with confirm dialog
- api.ts: updateDbPair, deleteDbPair

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

frontend/src/api.ts

@@ -453,3 +453,24 @@ export async function createDbPair(
   if (!res.ok) throw new Error(data.error || 'Fehler beim Erstellen des Pairs')
   return data
 }
+
+export async function updateDbPair(
+  pairId: string,
+  payload: { level?: number; question_de?: string; statement_de?: string },
+  token: string
+): Promise<void> {
+  const res = await fetch(`/api/directus/db-pairs/${pairId}`, {
+    method: 'PATCH',
+    headers: { 'Content-Type': 'application/json', Authorization: `Bearer ${token}` },
+    body: JSON.stringify(payload),
+  })
+  if (!res.ok) throw new Error('Fehler beim Aktualisieren des Pairs')
+}
+
+export async function deleteDbPair(pairId: string, token: string): Promise<void> {
+  const res = await fetch(`/api/directus/db-pairs/${pairId}`, {
+    method: 'DELETE',
+    headers: { Authorization: `Bearer ${token}` },
+  })
+  if (!res.ok) throw new Error('Fehler beim Löschen des Pairs')
+}