Add a no-op WailsUIReady RPC the UI probes once at startup. A reachable
daemon that returns Unimplemented predates this UI and is too old to
drive it; the probe distinguishes that from an unreachable daemon. On an
outdated daemon the UI fires a localized OS notification, since the main
window may not open to show an in-app error.
Proto regenerated with protoc 33.1 to keep the v6.33.1 header.
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