Add FastAPI backend with agent system

backend/app/schemas/todo.py

@@ -0,0 +1,40 @@
+from pydantic import BaseModel
+from datetime import datetime
+from app.models.todo import TodoSource
+
+
+class TodoCreate(BaseModel):
+    title: str
+
+
+class TodoUpdate(BaseModel):
+    title: str | None = None
+    is_completed: bool | None = None
+
+
+class TodoOut(BaseModel):
+    id: str
+    title: str
+    is_completed: bool
+    source: TodoSource
+    source_detail: str | None
+    todo_date: str
+    completed_at: datetime | None
+    created_at: datetime
+    updated_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class TodoListOut(BaseModel):
+    items: list[TodoOut]
+    total: int
+    page: int
+    page_size: int
+
+
+class TodoSummaryOut(BaseModel):
+    date: str
+    total: int
+    completed: int
+    pending: int