Add multi-user authentication with JWT

- Users table with email/bcrypt-hashed password; register and login via /auth/ endpoints
- JWT tokens (30-day expiry) stored in localStorage; all API routes require Bearer auth
- All data (varieties, batches, settings, notification logs) scoped to the authenticated user
- Login/register screen overlays the app; sidebar shows user email and logout button
- Scheduler sends daily ntfy summaries for every configured user
- DB schema rewritten for multi-user; SECRET_KEY added to env

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

docker-compose.yml

@@ -32,6 +32,7 @@ services:
       DB_NAME: sproutly
       DB_USER: ${MYSQL_USER}
       DB_PASSWORD: ${MYSQL_PASSWORD}
+      SECRET_KEY: ${SECRET_KEY}
     depends_on:
       mysql:
         condition: service_healthy