fix(training): switch to PAGE XML format for kurrent recognition training

Kraken 7 removed support for the legacy `path` format (image + .gt.txt
pairs) in VGSLRecognitionDataModule despite the CLI still advertising it.
Switching to PAGE XML (-f page) format which is the supported standard.

- Java export now writes .xml alongside .png (PAGE XML with TextLine,
  Baseline at 75% height, and Unicode transcription)
- XML special characters in transcription text are escaped (& < >)
- Python trainer globs *.xml and passes -f page to ketos train
- Regenerated frontend API types to include cer/loss/accuracy/epochs on
  OcrTrainingRun (were missing, causing empty CER column in history)
- Updated and extended TrainingDataExportServiceTest

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

frontend/src/lib/generated/api.ts

@@ -244,6 +244,22 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/api/ocr/segtrain": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get?: never;
+        put?: never;
+        post: operations["triggerSegTraining"];
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/api/ocr/batch": {
         parameters: {
             query?: never;
@@ -740,6 +756,22 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/api/ocr/segmentation-training-data/export": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get: operations["exportSegmentationTrainingData"];
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/api/ocr/jobs/{jobId}": {
         parameters: {
             query?: never;
@@ -1183,7 +1215,7 @@ export interface components {
             annotationId: string;
             /** Format: uuid */
             documentId: string;
-            text: string;
+            text?: string;
             label?: string;
             /** Format: int32 */
             sortOrder: number;
@@ -1247,6 +1279,14 @@ export interface components {
             /** Format: int32 */
             documentCount: number;
             modelName: string;
+            /** Format: double */
+            cer?: number;
+            /** Format: double */
+            loss?: number;
+            /** Format: double */
+            accuracy?: number;
+            /** Format: int32 */
+            epochs?: number;
             errorMessage?: string;
             /** Format: uuid */
             triggeredBy?: string;
@@ -1311,6 +1351,7 @@ export interface components {
         TriggerOcrDTO: {
             /** @enum {string} */
             scriptType?: "UNKNOWN" | "TYPEWRITER" | "HANDWRITING_LATIN" | "HANDWRITING_KURRENT";
+            useExistingAnnotations?: boolean;
         };
         CreateAnnotationDTO: {
             /** Format: int32 */
@@ -1473,18 +1514,18 @@ export interface components {
             /** Format: int32 */
             number?: number;
             sort?: components["schemas"]["SortObject"];
-            first?: boolean;
-            last?: boolean;
             /** Format: int32 */
             numberOfElements?: number;
+            first?: boolean;
+            last?: boolean;
             empty?: boolean;
         };
         PageableObject: {
+            paged?: boolean;
             /** Format: int32 */
             pageNumber?: number;
             /** Format: int32 */
             pageSize?: number;
-            paged?: boolean;
             /** Format: int64 */
             offset?: number;
             sort?: components["schemas"]["SortObject"];
@@ -2201,6 +2242,26 @@ export interface operations {
             };
         };
     };
+    triggerSegTraining: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Created */
+            201: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "*/*": components["schemas"]["OcrTrainingRun"];
+                };
+            };
+        };
+    };
     triggerBatch: {
         parameters: {
             query?: never;
@@ -3106,6 +3167,26 @@ export interface operations {
             };
         };
     };
+    exportSegmentationTrainingData: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description OK */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "*/*": components["schemas"]["StreamingResponseBody"];
+                };
+            };
+        };
+    };
     getJobStatus: {
         parameters: {
             query?: never;