feat: add streaming learning assistant and knowledge base scaffolding

app/schemas/learning_assistant.py

@@ -0,0 +1,36 @@
+from pydantic import BaseModel, Field
+
+
+class LearningAssistantChatRequest(BaseModel):
+    """学习助手请求：普通用户面向机构知识库提出医学学习问题。"""
+
+    question: str = Field(..., min_length=2, max_length=1000, description="用户问题")
+    top_k: int | None = Field(default=None, ge=1, le=10, description="最终返回给 LLM 的来源片段数")
+    score_threshold: float | None = Field(default=None, ge=0, le=1, description="向量相似度过滤阈值")
+
+
+class LearningAssistantSource(BaseModel):
+    """学习助手来源：记录 PDF 文档、页码和引用片段。"""
+
+    document_id: int
+    document_title: str | None = None
+    file_name: str
+    page_start: int
+    page_end: int
+    chunk_uid: str
+    score: float
+    quote: str
+
+
+class LearningAssistantChatResponse(BaseModel):
+    """学习助手回答：返回答案、知识库命中状态、循证来源和耗时。"""
+
+    answer: str
+    retrieval_hit: bool
+    sources: list[LearningAssistantSource] = Field(default_factory=list)
+    retrieval_error: str | None = None
+    model: str | None = None
+    embedding_latency_ms: int | None = None
+    search_latency_ms: int | None = None
+    llm_latency_ms: int | None = None
+    total_latency_ms: int | None = None