refactor: 将 MarkdownSplitter 移入 splitters 包，ingest.py 保留兼容 import

src/core/splitters/registry.py

@@ -0,0 +1,22 @@
+"""分块器注册表 — 按文件后缀名路由到对应 Splitter."""
+
+SUPPORTED_SUFFIXES: dict[str, str] = {
+    ".md": "markdown",
+    ".txt": "text",
+    ".html": "html",
+    ".pdf": "pdf",
+}
+
+_registry: dict[str, type] = {}
+
+
+def register_splitter(name: str, splitter_cls: type) -> None:
+    """注册一个分块器."""
+    _registry[name] = splitter_cls
+
+
+def get_splitter(name: str):
+    """获取已注册的分块器类."""
+    if name not in _registry:
+        raise ValueError(f"未注册的分块器: {name}")
+    return _registry[name]