11 tasks: the shared banner store + renderer, a friendlier
network-unreachable message in client.ts, then migrating every
existing inline error site (GarminConnection, SyncModal, Profile,
Activities, Analysis, TrainingTypesCard, LoginGate, OnboardingWizard)
to it, finishing with dead-CSS cleanup.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
