refactor(image): 重构水印处理逻辑以提高可维护性

- 移除 PhotoProcessContext 中的水印相关字段
- 新增 WatermarkConfig 类封装水印配置
- 修改 WatermarkStage 通过构造函数注入配置
- 调整 PrinterServiceImpl 中水印配置的传递方式
- 更新单元测试以适应新的配置注入方式
- 统一从配置对象读取水印参数而非上下文
- 优化日志记录与偏移量计算逻辑

src/test/java/com/ycwl/basic/image/pipeline/stages/WatermarkStageTest.java

@@ -3,6 +3,7 @@ package com.ycwl.basic.image.pipeline.stages;
 import com.ycwl.basic.image.pipeline.core.PhotoProcessContext;
 import com.ycwl.basic.image.pipeline.core.StageResult;
 import com.ycwl.basic.image.pipeline.enums.ImageType;
+import com.ycwl.basic.image.watermark.enums.ImageWatermarkOperatorEnum;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.*;
@@ -14,14 +15,18 @@ class WatermarkStageTest {
 
     @Test
     void testGetName() {
-        WatermarkStage stage = new WatermarkStage();
+        WatermarkConfig config = WatermarkConfig.builder().build();
+        WatermarkStage stage = new WatermarkStage(config);
 
         assertEquals("WatermarkStage", stage.getName());
     }
 
     @Test
     void testShouldExecute_NormalPhoto() {
-        WatermarkStage stage = new WatermarkStage();
+        WatermarkConfig config = WatermarkConfig.builder()
+                .watermarkType(ImageWatermarkOperatorEnum.PRINTER_DEFAULT)
+                .build();
+        WatermarkStage stage = new WatermarkStage(config);
 
         PhotoProcessContext context = PhotoProcessContext.builder()
                 .originalUrl("https://example.com/test.jpg")
@@ -34,7 +39,10 @@ class WatermarkStageTest {
 
     @Test
     void testShouldExecute_Puzzle_ShouldSkip() {
-        WatermarkStage stage = new WatermarkStage();
+        WatermarkConfig config = WatermarkConfig.builder()
+                .watermarkType(ImageWatermarkOperatorEnum.PRINTER_DEFAULT)
+                .build();
+        WatermarkStage stage = new WatermarkStage(config);
 
         PhotoProcessContext context = PhotoProcessContext.builder()
                 .originalUrl("https://example.com/puzzle.png")
@@ -47,7 +55,10 @@ class WatermarkStageTest {
 
     @Test
     void testShouldExecute_MobileUpload_ShouldSkip() {
-        WatermarkStage stage = new WatermarkStage();
+        WatermarkConfig config = WatermarkConfig.builder()
+                .watermarkType(ImageWatermarkOperatorEnum.PRINTER_DEFAULT)
+                .build();
+        WatermarkStage stage = new WatermarkStage(config);
 
         PhotoProcessContext context = PhotoProcessContext.builder()
                 .originalUrl("https://example.com/mobile.jpg")
@@ -60,7 +71,9 @@ class WatermarkStageTest {
 
     @Test
     void testExecute_NoWatermarkType_ShouldSkip() {
-        WatermarkStage stage = new WatermarkStage();
+        // 创建没有 watermarkType 的配置
+        WatermarkConfig config = WatermarkConfig.builder().build();
+        WatermarkStage stage = new WatermarkStage(config);
 
         PhotoProcessContext context = PhotoProcessContext.builder()
                 .originalUrl("https://example.com/test.jpg")