When HA sets a color via turn_on, also update the source's fallback_color
to match. This way when the api_input timeout fires (default 5s), the
stream reverts to the same color instead of black. turn_off resets
fallback to [0,0,0].
Added coordinator.update_source() for PUT /color-strip-sources/{id}.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>