refactor: remove security-related hooks and pages

- Deleted `useSecurity.ts` hook which managed authentication users, providers, and policies.
- Removed `Policies.tsx`, `Providers.tsx`, and `Users.tsx` pages that utilized the above hook.
- Cleaned up the `index.tsx` file in the Security section to remove references to the deleted pages.
- Updated mock data by removing unused properties related to forward authentication.

frontend/src/api/__tests__/proxyHosts.test.ts

@@ -37,8 +37,6 @@ describe('proxyHosts API', () => {
     hsts_subdomains: false,
     block_exploits: false,
     websocket_support: false,
-    forward_auth_enabled: false,
-    forward_auth_bypass: '',
     locations: [],
     enabled: true,
     created_at: '2023-01-01',