Add memory coach, transformer recall model, and training FAB.

Introduce Q/K/V memory dialogue with coach APIs, a lightweight NumPy
transformer for per-word forgetting prediction, and a floating training
menu linking daily quiz, spell, and coach flows.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/requirements.txt

@@ -7,3 +7,4 @@ pydantic==2.10.3
 pydantic-settings==2.6.1
 python-multipart==0.0.17
 pymysql==1.1.1
+numpy==2.0.2