fix(ai): correct double-wrap in OCR engine endpoints causing e.map error

Controller was returning { data: engines } which TransformInterceptor
wrapped again into { data: { data: engines } }. extractData() only peeled
one layer, leaving an object instead of the array — causing .map() to fail
in OcrEngineSelector.

- Return data directly from getOcrEngines() and selectOcrEngine()
- Add Array.isArray guard in OcrEngineSelector as defensive layer

frontend/components/admin/ai/OcrEngineSelector.tsx

@@ -22,7 +22,7 @@ export default function OcrEngineSelector() {
     try {
       setIsLoading(true);
       const data = await adminAiService.getOcrEngines();
-      setEngines(data);
+      setEngines(Array.isArray(data) ? data : []);
     } catch (_err: unknown) {
       toast.error('ไม่สามารถดึงข้อมูล OCR Engines ได้');
     } finally {