feat: 像素级扰动滤镜降低平台查重风险 (Issue #1765)

- generate_pixel_perturbation()：随机选 2-3 种滤镜组合
  - noise: 轻微噪声 (0.01~0.02)
  - unsharp: 锐化/柔化 (-0.5~+0.5)
  - curves: 对比度微调 (0.95~1.05)
  - color_balance: RGB 通道偏移
- _apply_pixel_perturbation()：渲染时追加到 FFmpeg filter chain
- edit_plan_service：批量变体生成时为每个变体生成不同像素扰动
- 参数幅度确保肉眼不可见（SSIM > 0.95），帧级差异 > 3%
- 11 个新测试覆盖滤镜组合/参数范围/验收

apps/worker/video_processing/unified_render_service.py

@@ -2227,12 +2227,17 @@ class UnifiedRenderService:
         perturbation = (self.plan.config or {}).get("visual_perturbation") or {}
         if not perturbation:
             return {}
-        return {
+        result = {
             "hflip": bool(perturbation.get("hflip", False)),
             "zoom_ratio": max(1.0, min(1.2, float(perturbation.get("zoom_ratio", 1.0) or 1.0))),
             "speed_factor": max(0.8, min(1.2, float(perturbation.get("speed_factor", 1.0) or 1.0))),
             "brightness_shift": max(-30, min(30, int(perturbation.get("brightness_shift", 0) or 0))),
         }
+        # #1765：同时读取像素级扰动滤镜
+        pixel_pert = (self.plan.config or {}).get("pixel_perturbation") or {}
+        if pixel_pert:
+            result["pixel_perturbation"] = pixel_pert
+        return result
 
     def _apply_visual_perturbation_pre_scale(self, filters: list[str], perturbation: dict) -> None:
         # scale+pad 之前的扰动（hflip），就地修改 filters
@@ -2250,6 +2255,48 @@ class UnifiedRenderService:
         brightness = perturbation.get("brightness_shift", 0)
         if brightness != 0:
             filters.append(f"eq=brightness={brightness / 100.0:.3f}")
+        
+        # #1765：追加像素级扰动滤镜
+        pixel_pert = perturbation.get("pixel_perturbation") or {}
+        if pixel_pert:
+            self._apply_pixel_perturbation(filters, pixel_pert)
+    
+    def _apply_pixel_perturbation(self, filters: list[str], pixel_pert: dict) -> None:
+        """应用像素级扰动滤镜（Issue #1765）。
+        
+        滤镜参数幅度确保肉眼不可见（SSIM > 0.95），但能让同素材不同变体
+        在帧级产生 > 3% 的差异，降低平台查重风险。
+        """
+        filter_list = pixel_pert.get("filters") or []
+        
+        for filt in filter_list:
+            if filt == "noise":
+                # 轻微噪声：noise=alls=0.015:allf=t+u
+                strength = pixel_pert.get("noise_strength", 0.015)
+                filters.append(f"noise=alls={strength}:allf=t+u")
+            
+            elif filt == "unsharp":
+                # 锐化/柔化：unsharp=3:3:amount
+                # amount > 0 锐化，< 0 柔化
+                amount = pixel_pert.get("unsharp_amount", 0.0)
+                if abs(amount) > 0.01:
+                    filters.append(f"unsharp=3:3:{amount:.2f}")
+            
+            elif filt == "curves":
+                # 对比度微调：curves 用 preset 或手动定义
+                # 简单方案：用 eq=contrast 代替（curves 语法复杂）
+                contrast = pixel_pert.get("curves_contrast", 1.0)
+                if abs(contrast - 1.0) > 0.01:
+                    filters.append(f"eq=contrast={contrast:.3f}")
+            
+            elif filt == "color_balance":
+                # RGB 通道偏移：color_balance=rs=...:gs=...:bs=...
+                r = pixel_pert.get("color_r", 0)
+                g = pixel_pert.get("color_g", 0)
+                b = pixel_pert.get("color_b", 0)
+                if r != 0 or g != 0 or b != 0:
+                    # color_balance 参数范围 -1.0 ~ 1.0，这里用 /100 转换
+                    filters.append(f"color_balance=rs={r/100:.3f}:gs={g/100:.3f}:bs={b/100:.3f}")
 
     @staticmethod
     def _clip_volume(clip: ResolvedClip) -> float: