fix: probe installed horizond during machine rejoin

[alongubkin]

Summary

• probe the installed horizond binary directly when checking machine connectivity
• bypass legacy machine-entrypoint wrappers that do not forward CLI arguments
• preserve fallback behavior for other service executable layouts

Why

Older machine bundles use machine-entrypoint as the service executable. Invoking that wrapper with status --json starts another daemon instead of returning status, so rejected credentials are incorrectly classified as an already-joined machine.

Testing

• cargo nextest run -p alien-deploy-cli --no-fail-fast (135 passed)
• regression test proves the legacy wrapper is not executed
• cargo fmt -p alien-deploy-cli --check

Strict workspace Clippy remains blocked by pre-existing warnings on main.

[greptile-apps]

Greptile Summary

This PR fixes machine rejoin connectivity checks for legacy installations by probing the installed horizond binary instead of invoking a machine-entrypoint wrapper that does not forward status arguments.

• Adds executable selection that uses a sibling horizond only for legacy machine-entrypoint service layouts.
• Preserves the configured service executable as the fallback for all other layouts.
• Adds a regression test confirming that the legacy wrapper is bypassed.

Confidence Score: 5/5

The PR appears safe to merge, with the targeted legacy-wrapper bypass covered by a regression test and fallback behavior retained.

The new selection is narrowly limited to a service executable named machine-entrypoint with an installed sibling horizond; otherwise the existing probe path remains unchanged.

Important Files Changed

Filename	Overview
crates/alien-deploy-cli/src/commands/join.rs	Routes legacy-wrapper connectivity probes to the sibling horizond binary and adds focused regression coverage; no actionable defect was established.

_{Reviews (1): Last reviewed commit: "fix: probe installed horizond during mac..." | Re-trigger Greptile}