fix: detect Tailscale for App Store CLI path and hung status checks

[Dimillian]

Motivation

• Tailscale detection fails for the macOS App Store build because the CLI executable lives at a lowercase .../MacOS/tailscale path and the code referenced the wrong-cased path.
• Long-running or stalled calls to the tailscale CLI could leave the frontend request hanging and the “Checking…” button disabled indefinitely.

Description

• Updated macOS binary candidate to include /Applications/Tailscale.app/Contents/MacOS/tailscale and adjusted the missing-binary message to reference the corrected path in src-tauri/src/tailscale/mod.rs.
• Added a shared timeout constant TAILSCALE_COMMAND_TIMEOUT (12s) and applied it to tailscale version (binary resolution) and tailscale status --json calls so slow or hung CLI calls return with an explicit timeout error.
• Propagated clear timeout and execution errors into the existing failure reporting so the caller/UI receives a useful error instead of hanging.
• Updated the macOS unit test expectation to assert the corrected lowercase App Store CLI path.

Testing

• Ran npm run typecheck which completed successfully.
• Ran cd src-tauri && cargo fmt to format changes locally.
• Attempted cd src-tauri && cargo check which failed in this container due to missing system glib-2.0 / pkg-config setup unrelated to the change, so full Rust build verification could not complete here.

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Codex Task

[Dimillian]

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Terminate tailscale child process when timeout elapses

resolve_tailscale_binary now wraps Command::output() in tokio::time::timeout, but when the deadline fires the future is dropped without killing/reaping the spawned process (Tokio Command defaults to kill_on_drop(false)), so a hung tailscale/launchctl invocation continues in the background even though this call returns; repeated checks can accumulate stray processes and eventually exhaust process slots. The same timeout pattern is also used in tailscale_status, so both call paths should explicitly kill/reap on timeout (or enable kill_on_drop(true)).

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