Bump build.zig.zon minimum_zig_version to 0.16.0 and update the Zig target string in CLAUDE.md, README.md, and docs/getting-started.md. Phase D of the 0.16.0 upgrade. Full suite green on 0.16.0: - zig build check — clean - zig build test — 47/47 pass - zig build test-integration — 18/18 pass - zig build test-stress — 14/14 pass - zig build cross-check — clean (linux/macos/windows-gnu) - All benchmark binaries compile (bench, scale-bench, bench-realistic, bench-tokio-parity, bench-runtime-zig, compare-bench, bench-micro-*). Plan: docs/superpowers/plans/2026-04-15-zig-0.16.0-upgrade.md (Tasks 16, 18). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>