fix(download): return author name instead of mid in _extract_author

- Fix download processor to return actual author name (e.g. "HOLA小测佬")
  instead of B站用户ID (mid, e.g. "406636263")
- Add 5 test cases for author extraction logic
- Resolves report display issue where UP主名称 showed numeric ID

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_processors/test_download.py

@@ -137,6 +137,7 @@ class TestDownloadProcessorMetadata:
         adapter.fetch_metadata = AsyncMock(return_value={
             "metadata": {
                 "title": "Test Video Title",
+                "author": "Test UP Author",
                 "mid": 12345,
                 "bvid": "BV1xx",
             },
@@ -347,6 +348,7 @@ class TestDownloadProcessorContent:
         adapter.fetch_metadata = AsyncMock(return_value={
             "metadata": {
                 "title": "Test Video Title",
+                "author": "Test Video Author",
                 "mid": 12345,
                 "bvid": "BV1xx",
                 "duration": 300,
@@ -481,3 +483,94 @@ class TestDownloadProcessorModuleExport:
         assert ParseProcessor is not None
         assert DownloadProcessor is not None
         assert ASRProcessor is not None
+
+
+class TestDownloadProcessorAuthorExtraction:
+    """Tests for _extract_author method - ensure it returns author name, not mid."""
+
+    def test_extract_author_returns_author_name_not_mid(self):
+        """_extract_author should return author name, not mid (user ID)"""
+        from kb_workflow.pipeline.processors.download import DownloadProcessor
+
+        processor = DownloadProcessor()
+
+        # Bilibili metadata with both author and mid
+        metadata = {
+            "metadata": {
+                "title": "Test Video",
+                "author": "HOLA小测佬",
+                "mid": 406636263,
+                "bvid": "BV1QXcCzfECp",
+            }
+        }
+
+        author = processor._extract_author(metadata, "bilibili")
+
+        # Should return author name, not mid
+        assert author == "HOLA小测佬"
+        assert author != "406636263"
+        assert author != str(metadata["metadata"]["mid"])
+
+    def test_extract_author_handles_nested_metadata(self):
+        """_extract_author should handle nested metadata structure"""
+        from kb_workflow.pipeline.processors.download import DownloadProcessor
+
+        processor = DownloadProcessor()
+
+        # Nested metadata structure
+        metadata = {
+            "metadata": {
+                "author": "Test Author Name",
+                "mid": 12345,
+            }
+        }
+
+        author = processor._extract_author(metadata, "bilibili")
+        assert author == "Test Author Name"
+
+    def test_extract_author_handles_flat_metadata(self):
+        """_extract_author should handle flat metadata structure"""
+        from kb_workflow.pipeline.processors.download import DownloadProcessor
+
+        processor = DownloadProcessor()
+
+        # Flat metadata structure (no nested 'metadata' key)
+        metadata = {
+            "author": "Flat Author",
+            "mid": 67890,
+        }
+
+        author = processor._extract_author(metadata, "bilibili")
+        assert author == "Flat Author"
+
+    def test_extract_author_handles_zhihu_platform(self):
+        """_extract_author should handle zhihu platform"""
+        from kb_workflow.pipeline.processors.download import DownloadProcessor
+
+        processor = DownloadProcessor()
+
+        # Zhihu metadata structure
+        metadata = {
+            "author": "Zhihu User",
+        }
+
+        author = processor._extract_author(metadata, "zhihu")
+        assert author == "Zhihu User"
+
+    def test_extract_author_returns_empty_string_for_missing_author(self):
+        """_extract_author should return empty string when author is missing"""
+        from kb_workflow.pipeline.processors.download import DownloadProcessor
+
+        processor = DownloadProcessor()
+
+        # Metadata without author
+        metadata = {
+            "metadata": {
+                "title": "Test Video",
+                "mid": 12345,
+            }
+        }
+
+        author = processor._extract_author(metadata, "bilibili")
+        assert author == ""
+