Fix backend deps and apply theme to all Cancel buttons

- Pin bcrypt==3.2.2 to fix passlib bcrypt backend detection error
- Add email-validator==2.2.0 required by Pydantic EmailStr
- Add btn-sm class to Cancel buttons in Admin, Dashboard, Log, Schedule views

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/requirements.txt

@@ -4,6 +4,8 @@ sqlalchemy[asyncio]==2.0.35
 aiomysql==0.2.0
 python-jose[cryptography]==3.3.0
 passlib[bcrypt]==1.7.4
+bcrypt==3.2.2
 pydantic-settings==2.5.2
 alembic==1.13.3
 python-multipart==0.0.12
+email-validator==2.2.0