ci(nix): reuse macOS release build for CLI smoke validation

[davidabram]

Pull request stack

Review and merge bottom-up. Each PR targets the previous PR's branch, so Files changed shows only that step's incremental changes.

Step	Pull request	Change
1/4	#308 — Faster Nix checks	Rust test-profile cache; deduplicate default MBT check
2/4	#309 — Quint workflow cleanup	Stop recompiling Rust MBT separately
3/4	#310 — macOS smoke-build reuse	Reuse release artifact for macOS smoke tests
4/4	#311 — CI timing summaries	Record Nix phase durations in job summaries

You are reviewing step 3/4: #310. Parent: #309. Next: #311.

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MacOS currently compiles a native release-profile dependency set again after the test-profile nix flake check (9m05 in #308), despite a parallel release validation job already building the same Darwin release-profile dependencies. Run the macOS CLI --help and version smoke checks on the binary produced by .#ci-checks in release validation, and skip the redundant native .#sce build in the macOS Nix CI job. Keep the Linux native smoke build unchanged (Linux release validation uses musl, not the native package).

Trade-off: macOS smoke tests the commit-bearing release build rather than the commit-independent developer package. The native development build remains manually buildable. Keep this draft until both macOS and Linux Nix CI pass and total job timing is measured.