fix: 修复develop分支Unit Tests 14个失败

YAML bug期间CI不触发，代码重构后测试未同步更新，导致14个单元测试失败。

修复内容：
1. video_processing/url_security.py: ALLOWED_VIDEO_MIME_TYPES已移至packages.domain，
   兼容层导入路径错误导致整个模块加载失败，连锁引发多个测试ImportError
2. test_multi_track_subtitle_concat.py: POSITION_ALIGNMENT已移至packages.domain.subtitle_style
3. test_classification.py: AssetLibraryKind新增IMAGE枚举，测试断言从2改为3

apps/worker/video_processing/url_security.py

@@ -9,7 +9,6 @@ from packages.shared.url_security import (  # noqa: F401
     ALLOWED_IMAGE_MIME_TYPES,
     ALLOWED_PORTS,
     ALLOWED_SCHEMES,
-    ALLOWED_VIDEO_MIME_TYPES,
     DEFAULT_MAX_DOWNLOAD_SIZE,
     MAX_URL_LENGTH,
     TRUSTED_DOMAINS,
@@ -19,3 +18,7 @@ from packages.shared.url_security import (  # noqa: F401
     safe_download_file,
     validate_url_safety,
 )
+
+from packages.domain.url_security import (  # noqa: F401
+    ALLOWED_VIDEO_MIME_TYPES,
+)

tests/unit/domain/test_classification.py

@@ -18,9 +18,9 @@ from packages.domain.classification import (
 class TestAssetLibraryKind:
     """AssetLibraryKind 枚举测试."""
 
-    def test_two_values(self):
-        """视频和配音两类."""
-        assert len(AssetLibraryKind) == 2
+    def test_three_values(self):
+        """视频/配音/图片三类."""
+        assert len(AssetLibraryKind) == 3
 
     def test_video(self):
         assert AssetLibraryKind.VIDEO == "video"
@@ -28,6 +28,9 @@ class TestAssetLibraryKind:
     def test_voice(self):
         assert AssetLibraryKind.VOICE == "voice"
 
+    def test_image(self):
+        assert AssetLibraryKind.IMAGE == "image"
+
     def test_str_compatible(self):
         """StrEnum 字符串兼容."""
         assert AssetLibraryKind.VIDEO == "video"

tests/unit/test_multi_track_subtitle_concat.py

@@ -468,7 +468,8 @@ class TestSubtitleStyle:
         assert style3.alignment == 5
 
     def test_9grid_positions(self):
-        from video_processing.subtitle_render_engine import POSITION_ALIGNMENT, SubtitleStyle
+        from packages.domain.subtitle_style import POSITION_ALIGNMENT
+from video_processing.subtitle_render_engine import SubtitleStyle
 
         for pos, align in POSITION_ALIGNMENT.items():
             style = SubtitleStyle.from_dict({"position": pos})