Enhance admin bootstrap process with reset functionality

- Update .env.example and README.md to include new ADMIN_BOOTSTRAP_RESET option for resetting admin credentials on startup.
- Modify main.py to implement logic for resetting the admin's password, role, and status if ADMIN_BOOTSTRAP_RESET is set to true.
- Adjust config.py to define the new setting, ensuring proper configuration management.

app/core/config.py

@@ -13,6 +13,9 @@ class Settings(BaseSettings):
     cookie_secure: bool = False
     admin_bootstrap_email: str = "admin@internal.local"
     admin_bootstrap_password: str = "ChangeMe123!"
+    # Wenn true: setzt Passwort/Rolle/Status des Bootstrap-Admins beim Start
+    # auf die .env-Werte zurück (auch wenn der User bereits existiert).
+    admin_bootstrap_reset: bool = False
 
     model_config = SettingsConfigDict(env_file=".env", env_file_encoding="utf-8")