feat: 添加 EPUBSplitter — ebooklib 提取章节文字后分块

- 新增 splitters/epub.py: ebooklib 读取 EPUB → BeautifulSoup 去标签 → TextSplitter 分块
- epub 作为可选依赖: uv sync --extra epub
- registry 新增 .epub 映射, ingest_file 处理 EPUB 二进制文件
- 测试: 3 个 EPUBSplitter 测试 (含空 EPUB/Protocol 合规)

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

pyproject.toml

@@ -18,21 +18,11 @@ dependencies = [
 md-vector-db = "src.cli.main:app"
 
 [project.optional-dependencies]
-dev = [
-    "pytest>=8.0",
-    "httpx>=0.27.0",
-]
-pdf = [
-    "pymupdf>=1.24.0",
-]
-html = [
-    "beautifulsoup4>=4.12.0",
-]
-all = [
-    "md-vector-db[pdf,html]",
-    "requests>=2.31.0",
-    "openai>=1.0.0",
-]
+dev = ["pytest>=8.0", "httpx>=0.27.0"]
+pdf = ["pymupdf>=1.24.0"]
+html = ["beautifulsoup4>=4.12.0"]
+epub = ["ebooklib>=0.18"]
+all = ["md-vector-db[pdf,html,epub]", "requests>=2.31.0", "openai>=1.0.0"]
 
 [build-system]
 requires = ["hatchling"]