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>

backend/schemas.py

@@ -1,10 +1,35 @@
 from __future__ import annotations
 from datetime import date, datetime
 from typing import Optional, List
-from pydantic import BaseModel
+from pydantic import BaseModel, EmailStr
 from models import Category, SunRequirement, WaterNeeds, BatchStatus
 
 
+# --- Auth ---
+
+class UserCreate(BaseModel):
+    email: EmailStr
+    password: str
+
+
+class UserLogin(BaseModel):
+    email: EmailStr
+    password: str
+
+
+class UserOut(BaseModel):
+    id: int
+    email: str
+    created_at: Optional[datetime] = None
+
+    model_config = {"from_attributes": True}
+
+
+class Token(BaseModel):
+    access_token: str
+    token_type: str
+
+
 # --- Variety ---
 
 class VarietyBase(BaseModel):