fix(custom-fields) : pass machineContextOnly through structure serialize/hydrate

- componentStructure: include machineContextOnly in save payload value object
- componentStructureHydrate: read machineContextOnly in hydrate and mapComponentCustomFields
- pieceProductStructure: include machineContextOnly in sanitize and hydrate

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/app/shared/model/componentStructure.ts

@@ -141,6 +141,7 @@ export const normalizeStructureForSave = (input: any): any => {
     const value: Record<string, any> = {
       type: field.type,
       required: !!field.required,
+      machineContextOnly: !!field.machineContextOnly,
     }
     if (field.options && field.options.length) {
       value.options = field.options

frontend/app/shared/model/componentStructureHydrate.ts

@@ -78,10 +78,18 @@ export const hydrateCustomFields = (fields: any[]): any[] => {
     const customFieldId = typeof field?.customFieldId === 'string' ? field.customFieldId : undefined
     const orderIndex = typeof field?.orderIndex === 'number' ? field.orderIndex : index
 
+    const machineContextOnly =
+      typeof field?.machineContextOnly === 'boolean'
+        ? field.machineContextOnly
+        : typeof valueObject?.machineContextOnly === 'boolean'
+          ? valueObject.machineContextOnly
+          : false
+
     return {
       name,
       type,
       required,
+      machineContextOnly,
       options,
       optionsText,
       defaultValue,
@@ -153,6 +161,7 @@ export const mapComponentCustomFields = (fields: any[]) => {
       name: typeof field?.name === 'string' ? field.name : '',
       type: field?.type ?? 'text',
       required: !!field?.required,
+      machineContextOnly: !!field?.machineContextOnly,
       options: Array.isArray(field?.options) ? field.options : [],
       optionsText: typeof field?.optionsText === 'string' ? field.optionsText : '',
       defaultValue,

frontend/app/shared/model/pieceProductStructure.ts

@@ -82,7 +82,7 @@ const sanitizePieceCustomFields = (fields: any[]): PieceModelCustomField[] => {
         options = parsed.length > 0 ? parsed : undefined
       }
 
-      const result: PieceModelCustomField = { name, type, required }
+      const result: PieceModelCustomField = { name, type, required, machineContextOnly: !!field?.machineContextOnly }
       if (options) {
         result.options = options
       }
@@ -131,6 +131,7 @@ const hydratePieceCustomFields = (fields: any[]): PieceModelStructureEditorField
     name: field?.name ?? '',
     type: field?.type ?? 'text',
     required: !!field?.required,
+    machineContextOnly: !!field?.machineContextOnly,
     options: Array.isArray(field?.options) ? field.options : undefined,
     optionsText: typeof field?.optionsText === 'string'
       ? field.optionsText