Split pearcord-drive/mux-wire into common/v1/v2/gossip modules with unchanged
barrel exports. Add dual-stack live smoke, view rpcWireVersion, and doc/CI
hardening. No behavior change; default PEARCORD_RPC_WIRE remains v1.
Move 136 prototype mixins under mixins/domain, json-export, and
runtime/* so the package root stays navigable. Manifest assign order
is unchanged; apply-platform-mixins and runtime registry paths updated.
Co-authored-by: Cursor <[email protected]>