cli-v0.1.0

ci/release: drop x86_64-apple-darwin from matrix

GHA macos-13 free-tier runner pool is exhausted in practice; the
v0.1.0 jobs sat in queue for 35+ minutes without runner pickup
while every other target completed. macOS 13 itself reached
end-of-life in November 2025. Intel Macs run the aarch64 build
under Rosetta with no measurable perf impact on the CLI's
workload, so the loss is purely operational.

Updates README install table, CONTRIBUTING release matrix, and
CHANGELOG to describe the 6-target desktop matrix.