Bring the docs/zig/** decision package and README 'Native Substrate
Direction' section into main, and record ADR-0196 (Accepted) as the
binding ratification.
The doctrine is explicitly NOT a wholesale Zig rewrite. It establishes a
ring architecture (Python = semantic source of truth; Rust = incumbent
algebra backend; Zig = Ring 1 native-substrate candidate only) and the
G0-G8 adoption gate ladder. Zig may enter only by clearing gates against
a locked reference contract; default-by-availability is forbidden.
ADR-0196 forward-references ADR-0180 as the first G1 instantiation (the
CRDT contract lock / ZC-0 slice). No Zig code is authorized.
