Replaces the fixed-type SimBridge::receive_inputs() with a tagged
receive() -> Option<Inbound>, where Inbound is Inputs(Vec<PlayerInput>) or
AtlasRequest(AtlasLayerRequest). A shared decode_inbound() demuxes a frame by
shape (msgpack array = inputs, map = atlas request) — additive, no wire change
to existing input/snapshot frames. Adds send_atlas_response() to the trait
(both TcpBridge + LocalBridge impls). receive_bridge_inputs routes inputs to
the InputQueue as before; atlas requests to a new AtlasRequestBuffer (drained
by the serve system next). Integration tests (bridge_tcp/bridge_ipc) updated to
the tagged receive(); a demux unit test covers all three branches.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>