feat: add PageIndex SDK with local/cloud dual-mode support (#207)

pageindex/parser/protocol.py

@@ -0,0 +1,28 @@
+from __future__ import annotations
+from dataclasses import dataclass
+from typing import Protocol, runtime_checkable
+
+
+@dataclass
+class ContentNode:
+    """Universal content unit produced by parsers."""
+    content: str
+    tokens: int
+    title: str | None = None
+    index: int | None = None
+    level: int | None = None
+    images: list[dict] | None = None  # [{"path": str, "width": int, "height": int}, ...]
+
+
+@dataclass
+class ParsedDocument:
+    """Unified parser output. Always a flat list of ContentNode."""
+    doc_name: str
+    nodes: list[ContentNode]
+    metadata: dict | None = None
+
+
+@runtime_checkable
+class DocumentParser(Protocol):
+    def supported_extensions(self) -> list[str]: ...
+    def parse(self, file_path: str, **kwargs) -> ParsedDocument: ...