支持画布生图选择抠图背景色

新增画布生图背景色选项并在角色、图标和 UI 素材提取入口展示选择控件。

将 screenColor 贯穿前端提交、后端请求解析、prompt 构建和生成后本地后处理调用。

保留角色动作旧绿幕路径，避免影响既有动画生成流程。

补充相关前后端单元测试和编辑器文档说明。

src/components/image-editor/ImageCanvasGenerationModel.ts

@@ -97,8 +97,20 @@ export const DEFAULT_ICON_DESCRIPTIONS = [
   '原图按钮',
   '冻结按钮',
 ];
+export const EDITOR_GENERATION_BACKGROUND_COLOR_OPTIONS = [
+  { label: '浅雾蓝', value: '#CFEFFF' },
+  { label: '浅钢蓝', value: '#B0C2E0' },
+  { label: '暖浅桃色', value: '#FFD6C2' },
+  { label: '淡薰衣草紫', value: '#E6D8FF' },
+  { label: '浅粉灰', value: '#F4D8E8' },
+  { label: '中度天蓝', value: '#7FB3FF' },
+] as const;
+export type EditorGenerationBackgroundColorValue =
+  (typeof EDITOR_GENERATION_BACKGROUND_COLOR_OPTIONS)[number]['value'];
+export const DEFAULT_EDITOR_GENERATION_BACKGROUND_COLOR =
+  EDITOR_GENERATION_BACKGROUND_COLOR_OPTIONS[0].value;
 export const UI_DESIGN_ASSET_EXTRACTION_PROMPT =
-  '仅提取被红色框框选的素材并整理成spritesheet，图集背景必须使用单一纯绿色 #00FF00 / RGB(0,255,0) 绿幕。绿幕背景必须平整无纹理、无渐变、无阴影、无地面、无环境、无道具，方便后续扣除背景；素材自身不要出现绿色描边、绿色底板、绿色投影或绿色反光。';
+  '仅提取被红色框框选的素材并整理成spritesheet，图集背景必须使用所选单一纯色抠图背景。纯色背景必须平整无纹理、无渐变、无阴影、无地面、无环境、无道具，方便后续扣除背景；素材自身不要出现与背景色相同或相近的描边、底板、投影或反光。';
 export const QUICK_EDIT_SIZE_PRESETS = [
   '1024x1024',
   '1536x1024',
@@ -547,6 +559,36 @@ export function getEditorImageModelDisplayName(
   );
 }
 
+export function normalizeEditorGenerationBackgroundColor(
+  value: string | null | undefined,
+): EditorGenerationBackgroundColorValue {
+  const normalizedValue = value?.trim().toUpperCase();
+  const normalizedHexValue = normalizedValue?.match(/#[0-9A-F]{6}/)?.[0];
+  const matched = EDITOR_GENERATION_BACKGROUND_COLOR_OPTIONS.find(
+    (option) =>
+      option.value === normalizedValue || option.value === normalizedHexValue,
+  );
+  return matched?.value ?? DEFAULT_EDITOR_GENERATION_BACKGROUND_COLOR;
+}
+
+export function getEditorGenerationBackgroundColorOption(
+  value: string | null | undefined,
+) {
+  const normalizedValue = normalizeEditorGenerationBackgroundColor(value);
+  return (
+    EDITOR_GENERATION_BACKGROUND_COLOR_OPTIONS.find(
+      (option) => option.value === normalizedValue,
+    ) ?? EDITOR_GENERATION_BACKGROUND_COLOR_OPTIONS[0]
+  );
+}
+
+export function formatEditorGenerationBackgroundColor(
+  value: string | null | undefined,
+) {
+  const option = getEditorGenerationBackgroundColorOption(value);
+  return `${option.label} ${option.value}`;
+}
+
 export function buildQuickEditModelOptions(currentModel: string) {
   const normalizedCurrentModel = normalizeEditorImageModel(currentModel);
   const options = [...QUICK_EDIT_MODEL_OPTIONS];
@@ -1077,9 +1119,16 @@ export function buildCharacterGenerationInputs(
   prompt: string,
   specReference: CharacterReferenceImage | null | undefined,
   references: CharacterReferenceImage[] | undefined,
+  screenColor?: string,
 ): CanvasGenerationInputs {
   return {
-    fields: createGenerationInputField('角色设定', prompt),
+    fields: [
+      ...createGenerationInputField('角色设定', prompt),
+      ...createGenerationInputField(
+        '抠图背景色',
+        formatEditorGenerationBackgroundColor(screenColor),
+      ),
+    ],
     references: [
       ...(specReference
         ? createGenerationInputReference('角色规范', specReference)
@@ -1184,6 +1233,7 @@ export function buildIconGenerationInputs(
   iconDescriptions: string[],
   specReference: CharacterReferenceImage,
   references?: CharacterReferenceImage[],
+  screenColor?: string,
 ): CanvasGenerationInputs {
   return {
     fields: [
@@ -1191,6 +1241,10 @@ export function buildIconGenerationInputs(
         title: '素材描述',
         value: iconDescriptions.join('\n'),
       },
+      ...createGenerationInputField(
+        '抠图背景色',
+        formatEditorGenerationBackgroundColor(screenColor),
+      ),
     ],
     references: [
       ...createGenerationInputReference('图标规范', specReference),
@@ -1204,12 +1258,19 @@ export function buildIconGenerationInputs(
 export function buildUiDesignAssetExtractionGenerationInputs(
   sourceLayer: CanvasLayer,
   references?: CharacterReferenceImage[],
+  screenColor?: string,
 ): CanvasGenerationInputs {
   return {
-    fields: createGenerationInputField(
-      '提取提示词',
-      UI_DESIGN_ASSET_EXTRACTION_PROMPT,
-    ),
+    fields: [
+      ...createGenerationInputField(
+        '提取提示词',
+        UI_DESIGN_ASSET_EXTRACTION_PROMPT,
+      ),
+      ...createGenerationInputField(
+        '抠图背景色',
+        formatEditorGenerationBackgroundColor(screenColor),
+      ),
+    ],
     references: [
       ...createLayerGenerationInputReference('UI设计图', sourceLayer),
       ...(references ?? []).flatMap((reference, index) =>