refactor(ocr): return TrainingInfoResponse directly from getTrainingInfo endpoint

Remove the intermediate Map<String,Object> and return the typed record directly
so OpenAPI codegen produces a concrete TypeScript type. Fixes lastRun serializing
as {} (empty object) instead of null when no training run exists.

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

backend/src/test/java/org/raddatz/familienarchiv/controller/OcrControllerTest.java

@@ -264,6 +264,18 @@ class OcrControllerTest {
                 .andExpect(jsonPath("$.personNames." + personId).value("Max Mustermann"));
     }
 
+    @Test
+    @WithMockUser(authorities = "ADMIN")
+    void getTrainingInfo_serializes_null_lastRun_as_json_null() throws Exception {
+        OcrTrainingService.TrainingInfoResponse info =
+                new OcrTrainingService.TrainingInfoResponse(0, 0, 0, 0, false, null, List.of(), Map.of());
+        when(ocrTrainingService.getTrainingInfo()).thenReturn(info);
+
+        mockMvc.perform(get("/api/ocr/training-info"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.lastRun").doesNotExist());
+    }
+
     @Test
     @WithMockUser(authorities = "READ_ALL")
     void getDocumentOcrStatus_returnsNone_whenNoOcrJobExists() throws Exception {