Bulk-replace schematic + pid grounding

Overwrites grounding_data atomically with a versioned codec dict. Accepts either a v0 envelope ({version: 'v0', schematic, pid}), a v1 envelope ({version: 'v1', network, annotations, ...}), or a bare legacy {schematic, pid} body (treated as unversioned v0 for backward compatibility with pre-codec frontend builds). The version is sniffed off the body — no separate endpoint per format.