fix(settings): handle invalid session token on sign out

[vpomerleau]

Because

• If the session token no longer exists on the server, sessionDestroy returns 401/errno 110 and the avatar-menu toast strands the user with stale local state.

This pull request

• Swallows errno 110 in Session.destroy() so local cleanup and redirect proceed. Other errors still surface the toast.
• Adds tests for Session.destroy().

Issue that this pull request solves

Closes: FXA-13685

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[Copilot]

Pull request overview

This PR updates the fxa-settings sign-out/session teardown path so that local sign-out cleanup still completes when the server reports the session token is already invalid (401 / errno 110), avoiding users being stranded with stale local state.

Changes:

• Swallow ERRNO.INVALID_TOKEN errors from authClient.sessionDestroy() so local cleanup + redirect can proceed.
• Add unit tests covering success, INVALID_TOKEN, other failures, and “no session token” behavior for Session.destroy().

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/fxa-settings/src/models/Session.ts	Catch and ignore ERRNO.INVALID_TOKEN from sessionDestroy while preserving rethrow behavior for all other errors.
packages/fxa-settings/src/models/Session.test.ts	Adds coverage for the new destroy() error-handling behavior and existing cleanup semantics.

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