fix: remove HeaderAuthorization from forward-auth endpoint

Only use CookieSession strategy for forward-auth endpoint to ensure
browsers receive proper 302 redirects to the login page instead of
HTTP Basic auth prompts.

When HeaderAuthorization is in the strategies list, it sends
www-authenticate headers that trigger browser Basic auth dialogs.
For browser-based authentication, we only want CookieSession which
handles redirects properly.

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

net/authelia/configuration.yml

@@ -15,7 +15,6 @@ server:
         implementation: 'ForwardAuth'
         authn_strategies:
           - name: 'CookieSession'
-          - name: 'HeaderAuthorization'
 
 log:
   level: info