routerProvider was watching authProvider and returning a new GoRouter
on every status transition (unknown → authenticated). This caused
MaterialApp.router to rebuild the entire navigation tree, which
triggered all data providers to start loading before auth was confirmed.
Switch to refreshListenable pattern: GoRouter is created once,
_RouterNotifier fires notifyListeners() when auth changes, and GoRouter
re-runs redirect using ref.read(authProvider). Add /loading splash route
shown during AuthStatus.unknown so no authenticated screen (and no API
call) is initiated until the stored-token check completes.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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