host-ch32: rest PB10 as input pull-up, adapter-side mark source - #64
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The bus wire previously rested as AF open-drain, leaving idle mark entirely to a DUT-side pull-up - a bare adapter could not hold the wire high. PB10 now rests as input pull-up, putting the V305's internal ~40k on the wire whenever the adapter is not driving. The USART receiver samples the pad fine in input mode under HDSEL, and every transmission including the break happens inside a claim window (bus_drive push-pull), so the input rest state never eats outgoing bits.
The ~40k holds idle mark only; a long multi-drop harness still wants the external bench 10k.
Benched on a WCH-LinkE adapter against a dev-v006 board at 1M: discover, 5/5 pings, status, register clear - crc_fail 0, framing_drop 0.