test: 补充缺失的核心模块测试，统一CLI测试行为

新增测试文件：
- tests/test_core/test_parser.py - 测试 parse_input/process_content/output_result
- tests/test_core/test_markdown_extra.py - 测试 extract_title_content/search_markdown
- tests/test_utils/test_encoding_detection.py - 测试编码检测模块
- tests/test_readers/test_html_downloader.py - 测试HTML下载器

修改：
- tests/conftest.py - 移除pytest.skip()，所有CLI测试在缺少依赖时直接失败（与HTML测试行为一致）

tests/conftest.py

@@ -51,10 +51,7 @@ def temp_docx(tmp_path):
         str: 临时文件路径
     """
     def _create_docx(paragraphs=None, headings=None, table_data=None, list_items=None):
-        try:
-            from docx import Document
-        except ImportError:
-            pytest.skip("python-docx 未安装")
+        from docx import Document
 
         doc = Document()
 
@@ -99,13 +96,10 @@ def temp_pdf(tmp_path):
         str: 临时文件路径
     """
     def _create_pdf(text=None, lines=None):
-        try:
-            from reportlab.pdfgen import canvas
-            from reportlab.lib.pagesizes import letter
-            from reportlab.pdfbase import pdfmetrics
-            from reportlab.pdfbase.ttfonts import TTFont
-        except ImportError:
-            pytest.skip("reportlab 未安装")
+        from reportlab.pdfgen import canvas
+        from reportlab.lib.pagesizes import letter
+        from reportlab.pdfbase import pdfmetrics
+        from reportlab.pdfbase.ttfonts import TTFont
 
         file_path = tmp_path / "test.pdf"
         c = canvas.Canvas(str(file_path), pagesize=letter)
@@ -176,10 +170,7 @@ def temp_pptx(tmp_path):
         str: 临时文件路径
     """
     def _create_pptx(slides=None):
-        try:
-            from pptx import Presentation
-        except ImportError:
-            pytest.skip("python-pptx 未安装")
+        from pptx import Presentation
 
         prs = Presentation()
 
@@ -209,10 +200,7 @@ def temp_xlsx(tmp_path):
         str: 临时文件路径
     """
     def _create_xlsx(data=None):
-        try:
-            import pandas as pd
-        except ImportError:
-            pytest.skip("pandas 未安装")
+        import pandas as pd
 
         file_path = tmp_path / "test.xlsx"