refactor: 将核心代码迁移到 scripts 目录

- 创建 scripts/ 目录作为核心代码根目录
- 移动 core/, readers/, utils/ 到 scripts/ 下
- 移动 config.py, lyxy_document_reader.py 到 scripts/
- 移动 encoding_detection.py 到 scripts/utils/
- 更新 pyproject.toml 中的入口点路径和 pytest 配置
- 更新所有内部导入语句为 scripts.* 模块
- 更新 README.md 目录结构说明
- 更新 openspec/config.yaml 添加目录结构说明
- 删除无用的 main.py

此变更使项目结构更清晰，便于区分核心代码与测试、文档等支撑文件。

scripts/core/__init__.py

@@ -0,0 +1,47 @@
+"""Core module for lyxy-document."""
+
+from .exceptions import (
+    LyxyDocumentError,
+    FileDetectionError,
+    ReaderNotFoundError,
+    ParseError,
+    DownloadError,
+)
+from .markdown import (
+    parse_with_markitdown,
+    parse_with_docling,
+    build_markdown_table,
+    flush_list_stack,
+    safe_open_zip,
+    normalize_markdown_whitespace,
+    remove_markdown_images,
+    get_heading_level,
+    extract_titles,
+    extract_title_content,
+    search_markdown,
+    _unstructured_elements_to_markdown,
+)
+from .parser import parse_input, process_content, output_result
+
+__all__ = [
+    "LyxyDocumentError",
+    "FileDetectionError",
+    "ReaderNotFoundError",
+    "ParseError",
+    "DownloadError",
+    "parse_with_markitdown",
+    "parse_with_docling",
+    "build_markdown_table",
+    "flush_list_stack",
+    "safe_open_zip",
+    "normalize_markdown_whitespace",
+    "remove_markdown_images",
+    "get_heading_level",
+    "extract_titles",
+    "extract_title_content",
+    "search_markdown",
+    "_unstructured_elements_to_markdown",
+    "parse_input",
+    "process_content",
+    "output_result",
+]