feat: 完善 AI-Core 文档解析器

- 添加多种文档解析器 (PDF, Word, Excel, Markdown 等)
- 添加基础解析器和链式解析器
- 添加存储和注册机制
- 添加 gRPC 服务实现

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ai-core/parser/base_parser.py

@@ -0,0 +1,61 @@
+# -*- coding: utf-8 -*-
+import logging
+import os
+from abc import ABC, abstractmethod
+from typing import Optional
+
+from docreader.models.document import Document
+
+logger = logging.getLogger(__name__)
+logger.setLevel(logging.INFO)
+
+
+class BaseParser(ABC):
+    """Base parser interface.
+
+    After the lightweight refactoring, BaseParser only extracts markdown text
+    and raw image references from documents. Chunking, image storage, OCR,
+    and VLM caption are handled by the Go App module.
+    """
+
+    def __init__(
+        self,
+        file_name: str = "",
+        file_type: Optional[str] = None,
+        **kwargs,
+    ):
+        self.file_name = file_name
+        self.file_type = file_type or os.path.splitext(file_name)[1].lstrip(".")
+
+        logger.info(
+            "Initializing parser for file=%s, type=%s",
+            file_name,
+            self.file_type,
+        )
+
+    @abstractmethod
+    def parse_into_text(self, content: bytes) -> Document:
+        """Parse document content into markdown text.
+
+        Returns:
+            Document with ``content`` (markdown string) and optional
+            ``images`` dict mapping storage-relative paths to base64 data.
+        """
+
+    def parse(self, content: bytes) -> Document:
+        """Parse document and return markdown + image references.
+
+        No chunking, no OCR, no VLM caption — those are done in Go.
+        """
+        logger.info(
+            "Parsing document with %s, bytes: %d",
+            self.__class__.__name__,
+            len(content),
+        )
+        document = self.parse_into_text(content)
+        logger.info(
+            "Extracted %d characters from %s",
+            len(document.content),
+            self.file_name,
+        )
+        return document