[corpus] Land build-forge contract pack + build_forge_tritrpc_v0_1.proto

[mdheller]

Stand up the build-forge contract pack (build_forge_contract_pack_v0_1.md + .schema.json) and the ternary-native build_forge_tritrpc_v0_1.proto in TriTRPC. Extract from extracted/build_forge_contract_bundle_v0_1/ (3 files). Follow the schema+validator pattern used across the tranche work. Captured at ~/dev/spec-intake/2026-07-31/ (see PROGRAM_SPEC_REGISTER.md; register mirrored on sourceos-spec branch capture/spec-intake-register-2026-07-31). Part of the Agentic-Stack program (epic SocioProphet/socioprophet#490).