fix(mobile): don't block app open on slow validateAccessToken (#28405)

* fix(mobile): don't block app open on slow validateAccessToken

AuthGuard.onNavigation was async so auto_route awaited the body through validateAccessToken's OS timeout. now it's sync and the validate runs in bg. kicks to login on 401.

* fix(mobile): handle re-login race in AuthGuard validate

if user logs out + logs back in during a slow validate, the old 401 was logging them out again. now we check the token hasn't changed before redirecting, and dedupe in-flight calls.

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Co-authored-by: Alex <alex.tran1502@gmail.com>