acp: Simplify auth check and allow for custom /logout commands (#39867)

- Prefer agent-specific logout handling to allow state reset 
- Treat any auth method as supported; remove provider-specific filter 
- Avoid prompting auth when issuing /logout and agent supports it

Release Notes:

- N/A
f1d17fcfbeBen Brandt committed on 10/9/2025, 12:58:59 PM· committed by GitHubparentccfc1ce
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