Add admin UI to view and toggle resource slot type enablement

## Background

After migrating to 26.4.9, every device row in the `resource_slot_types` table ends up `enabled`. In enterprise environments where fGPU is in use, session creation then fails because the `cuda.device` resource condition cannot be satisfied.

The current workaround is to set `enabled = false` for `cuda.device` directly in the database. Requiring direct DB access for this is not acceptable — the setting should be exposed through an admin menu in WebUI.

## Scope

- Add an admin-only screen listing resource slot types with their current enabled state.
- Allow an admin to enable/disable each slot type.
- Consume the backend read/update API for `resource_slot_types` (no such API exists today; it is being added separately on the backend side).

## Notes

- Placing this in the Control Panel was considered, but the WebUI admin menu is the agreed target.
- Blocked on the backend API work — implementation cannot start until the API lands.

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Captured while working on branch: feat/FR-3376-check2-backlog

JIRA Issue: FR-3470

Start at the WebUI admin menu and review how existing admin screens consume backend APIs. Once the resource_slot_types read/update API lands, use it to list each slot type and its enabled state and provide per-type toggles. Done means admins can view and change enablement without direct database access.

Written by the indexing model from the issue text.