fix(autostart): prepare FreeBSD executable integration

[vincentkoc]

Prepare FreeBSD executable-path integration from tauri-apps#3440, preserving contributor credit and retaining auto-launch 0.5 on every existing platform.

This draft remains blocked on an upstream dependency release. Published auto-launch 0.6.0 predates both the FreeBSD implementation merged in zzzgydi/auto-launch#38 at 5a77b66cfb745e2ead928fe37aedee828cb993ea and the subsequent XDG argument-quoting fix merged in zzzgydi/auto-launch#39. A released crate containing both is required before the FreeBSD dependency requirement can be finalized. The development-only FreeBSD proof below uses the tauri-apps#38 merge and does not qualify tauri-apps#39. This source branch contains no dependency override.

The regression fixture uses a child process with a disposable HOME and checks the actual plugin's XDG enable, re-enable, is-enabled and disable behavior, including executable arguments and removal of the desktop entry.

Validation:

• Native Linux passed cargo test --locked -p tauri-plugin-autostart --lib --test xdg at f11740c97c32c120da89302bff94b0018b0bb8b5 on a disposable secretless Crabbox. Cargo selected registry auto-launch 0.5.0. The original lock hash remained b069b475db038fcacfd5578da766a60bd4e99e70faa78779215bf4716ebd8c78.
• Native FreeBSD passed the same test in an explicitly unreleased development composition: proof-only commit 748cc3632f4f8847ac04bcbd2752a78c12e1a0b6 changes only Cargo.lock from this draft, with reviewed hash 0a2d9dbd4f90e0956e692fa267cdd62eef0507db0f9d2ef29957e421d5e9710e. Ephemeral Cargo CLI patch arguments selected the exact canonical auto-launch commit 5a77b66cfb745e2ead928fe37aedee828cb993ea. FreeBSD receipt, attempt 1, verifies the source, parent, locks, native dependency selection and unchanged checkout after testing.
• Both runs used Rust 1.98.1; the real fixture's parent and child each passed with zero ignored tests. Independent source, lock and native-proof review completed. This covers XDG entry management, not desktop login/session or GUI launch.

The normal lock-only commit records published-dependency resolution from cargo update --workspace. Review confirmed that all 34 records and resolved edges in the existing auto-launch 0.5 closure are unchanged. The added 0.6 closure requires two objc2 updates in this test workspace; the entire macOS workspace lock is not byte-identical. The separate proof composition also preserves the complete 0.5 closure and is not included in this draft.

Local rustfmt, TOML and whitespace checks passed. The successful development composition does not establish registry-only FreeBSD support or release readiness. No release version is invented or published.

Metadata follow-up at 1f1c42542790ed728d3d26fc2a6f8d5252e9d58d: the existing change-file and new-file license checks pass on a disposable, secretless Linux Crabbox. The original inputs reproduced the expected failures. This follow-up adds the required paired JavaScript changeset entries where applicable and uses the repository-required test headers; production code, dependency resolution, test logic, and CI workflows are unchanged. Native behavior evidence above remains bound to its recorded revision.

The corrected head passes the change-file, license-header, formatting, and Covector checks. Rust audit separately fails on inherited rustls 0.23.28 under RUSTSEC-2026-0285, disclosed September 14; the advisory identifies 0.23.45 as patched. The complete rustls lock record and incoming dependency references are unchanged from base 0850317b5c85092cbf4ea9caf4ef3a9c771fcf27, through the original candidate and this metadata correction. Follow-up: refresh the upstream workspace's affected dependency lock before claiming a green audit. The audit has not been ignored or disabled.