Make auto deny TTL an admin configurable setting

The application currently uses a fixed TTL value of 3 days for auto deny behavior. This value is hard coded and cannot be adjusted without code changes. We need to make this TTL configurable by administrators so organizations can tune the behavior based on their governance and workflow requirements.

**Current behavior:**

* Auto deny TTL is set to 3 days.
* TTL value is not configurable through admin settings.
* Changing the TTL requires code modification and redeployment.

**Requested change:**

* Introduce an admin configurable setting for auto deny TTL.
* Allow admins to define TTL value in days.
* Provide a sensible default of 3 days for existing deployments.
* Validate TTL input to prevent invalid or extreme values.

The issue names no files, tests, or entry points. Start by locating the hard-coded three-day auto-deny TTL and the existing admin settings flow, then inspect how settings are validated and persisted. Done means administrators can set a validated day-based TTL, while existing deployments retain a default of three days.

Written by the indexing model from the issue text.