feat: add document file download and admin page file display

1. 新增将文档元数据存入L1向量库的功能
2. 新增文档文件下载API接口，支持路径安全校验
3. 后端文档详情接口新增文件信息返回字段
4. 管理后台页面新增原始文件信息展示与下载链接

app/services/qdrant.py

@@ -9,6 +9,7 @@
 """
 
 import uuid
+from pathlib import Path
 from typing import Any
 
 import structlog
@@ -103,18 +104,50 @@ class QdrantService:
         tags: list[str],
         dense_vector: list[float],
         sparse_vector: SparseVectorTuple | None = None,
+        metadata: dict[str, str] | None = None,
     ) -> None:
-        """写入 L1 文档总结，payload 含 doc_id/title/category/tags/text(=summary)"""
+        """写入 L1 文档总结，payload 含 doc_id/title/category/tags/text(=summary)/metadata
+
+        metadata 默认 None 时存空 dict，保证字段始终存在；存量旧文档读取时按缺失处理。
+        """
         vector: dict[str, Any] = {VECTOR_DENSE: dense_vector}
         if sparse_vector is not None:
             vector[VECTOR_SPARSE] = models.SparseVector(indices=sparse_vector[0], values=sparse_vector[1])
         point = models.PointStruct(
             id=_point_id(f"{doc_id}:l1"),
             vector=vector,
-            payload={"doc_id": doc_id, "title": title, "category": category, "tags": tags, "text": summary},
+            payload={
+                "doc_id": doc_id,
+                "title": title,
+                "category": category,
+                "tags": tags,
+                "text": summary,
+                "metadata": metadata or {},
+            },
         )
         await self._client.upsert(collection_name=COLLECTION_L1, points=[point])
 
+    async def get_l1_metadata(self, doc_id: str) -> dict[str, str] | None:
+        """按 doc_id 查 L1 点，返回其 payload.metadata
+
+        文档不存在或 payload 无 metadata 字段时返回 None。
+        """
+        doc_filter = self.build_filter(doc_ids=[doc_id])
+        records, _ = await self._client.scroll(
+            collection_name=COLLECTION_L1,
+            scroll_filter=doc_filter,
+            limit=1,
+            with_payload=True,
+            with_vectors=False,
+        )
+        if not records:
+            return None
+        payload = records[0].payload or {}
+        meta = payload.get("metadata")
+        if not isinstance(meta, dict):
+            return None
+        return meta
+
     async def upsert_nodes(self, collection: str, nodes: list[dict[str, Any]]) -> None:
         """批量写入 L2/L3 大纲节点
 
@@ -252,7 +285,12 @@ class QdrantService:
         return items, str(next_offset) if next_offset is not None else None
 
     async def get_doc_detail(self, doc_id: str) -> dict[str, Any] | None:
-        """获取文档详情：L1 记录 + L2/L3 全部节点 + chunks 数量，文档不存在返回 None"""
+        """获取文档详情：L1 记录 + L2/L3 全部节点 + chunks 数量 + file 文件信息
+
+        file 字段从 L1 payload.metadata 提取（raw_file_path/original_filename/original_size_bytes）：
+        有 raw_file_path 时返回 {filename, size_bytes, url}，否则 None。
+        文档不存在返回 None。
+        """
         doc_filter = self.build_filter(doc_ids=[doc_id])
         l1_records, _ = await self._client.scroll(
             collection_name=COLLECTION_L1,
@@ -271,11 +309,23 @@ class QdrantService:
             count_filter=doc_filter,
             exact=True,
         )
+
+        # 从 L1 metadata 提取原始文件信息，无 raw_file_path 时 file=None
+        meta = (l1_records[0].payload or {}).get("metadata") or {}
+        raw_path = meta.get("raw_file_path", "")
+        file_info: dict[str, Any] | None = None
+        if raw_path:
+            file_info = {
+                "filename": meta.get("original_filename", Path(raw_path).name),
+                "size_bytes": int(meta.get("original_size_bytes", "0") or "0"),
+                "url": f"/api/v1/documents/{doc_id}/file",
+            }
         return {
             "l1": l1_records[0].payload or {},
             "l2_nodes": l2_nodes,
             "l3_nodes": l3_nodes,
             "chunks_count": chunks_count.count,
+            "file": file_info,
         }
 
     async def delete_by_doc_id(self, doc_id: str) -> dict[str, int]: