style: format backend with black

Also drops the session-sliding comment in login_required.

backend/notes.py

@@ -1,4 +1,5 @@
 """Notes slice: a per-book reading journal. Ownership is always derived through books.user_id."""
+
 from flask import Blueprint, g, jsonify
 
 from auth import login_required
@@ -22,7 +23,12 @@ def to_json(row: dict) -> dict:
 
 
 def _require_book(book_id: int) -> None:
-    if query_one("SELECT 1 FROM books WHERE id = %s AND user_id = %s", (book_id, g.user_id)) is None:
+    if (
+        query_one(
+            "SELECT 1 FROM books WHERE id = %s AND user_id = %s", (book_id, g.user_id)
+        )
+        is None
+    ):
         raise ApiError(404, "Book not found")
 
 
@@ -42,7 +48,10 @@ def list_notes(book_id: int):
 def add_note(book_id: int):
     _require_book(book_id)
     body = text(json_body({"body"}), "body", MAX_BODY)
-    row = query_one(f"INSERT INTO notes AS n (book_id, body) VALUES (%s, %s) RETURNING {NOTE_COLUMNS}", (book_id, body))
+    row = query_one(
+        f"INSERT INTO notes AS n (book_id, body) VALUES (%s, %s) RETURNING {NOTE_COLUMNS}",
+        (book_id, body),
+    )
     return jsonify(to_json(row)), 201