feat(auth): add authenticated redirect fallback

[onmax]

Summary

• Add new auth.redirects.authenticated config option for post-login/sign-up default navigation.
• Route post-auth flow in useUserSession to resolve onSuccess → query redirect → authenticated fallback, with local-path safety checks.
• Keep middleware semantics unchanged for auth.redirects.login and auth.redirects.logout.
• Update config serialization endpoint to expose the new field.
• Extend tests and docs for configuration, precedence, and default no-op behavior.

Testing

• Added coverage in test/wrap-auth-method.test.ts.
• Added coverage in test/use-user-session.test.ts.
• Added runtime config endpoint coverage in test/redirects-option.test.ts.

No full suite run in this commit.

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commit: 4145ab1