Add super admin panel and update README

- Admin account bootstrapped from ADMIN_EMAIL/ADMIN_PASSWORD env vars on startup
- Admin panel: list users, view content, reset passwords, disable/delete accounts
- is_admin and is_disabled columns on users table
- Disabled accounts blocked at login
- README updated with admin setup instructions and panel docs

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

backend/schemas.py

@@ -13,18 +13,34 @@ class UserCreate(BaseModel):
 
 
 class UserLogin(BaseModel):
-    email: EmailStr
+    email: str
     password: str
 
 
 class UserOut(BaseModel):
     id: int
     email: str
+    is_admin: bool = False
+    is_disabled: bool = False
     created_at: Optional[datetime] = None
 
     model_config = {"from_attributes": True}
 
 
+class AdminUserOut(BaseModel):
+    id: int
+    email: str
+    is_admin: bool
+    is_disabled: bool
+    created_at: Optional[datetime]
+    variety_count: int
+    batch_count: int
+
+
+class AdminResetPassword(BaseModel):
+    new_password: str
+
+
 class Token(BaseModel):
     access_token: str
     token_type: str