feat(macos): add TrayIconAttributes::autosave_name for NSStatusItem position persistence

[ericwang915]

Problem

The macOS impl creates the NSStatusItem without calling setAutosaveName. AppKit therefore can't persist the user's ⌘+drag position across launches via NSUserDefaults, so the status item resets to the default leftmost slot every launch.

On notched MacBooks (M1+ Pro/Max, 14"/16") that default slot is directly under the camera cutout — the icon is partially or fully obscured, and there's no permanent fix the user can apply.

Solution

Add an opt-in autosave_name: Option<String> to TrayIconAttributes plus a with_autosave_name builder method. When set, the macOS impl forwards it to NSStatusItem.setAutosaveName. AppKit then handles position persistence automatically:

let tray = TrayIconBuilder::new()
    .with_autosave_name("com.example.app.tray")
    .with_icon(icon)
    .build()?;

The key should be a stable, app-unique string (typically reverse-DNS); changing it invalidates the saved position. No-op on Linux / Windows.

Why opt-in (not always-on)

Default-on would require synthesizing an autosave key from TrayIconId, but TrayIconId defaults to a counter-generated string (COUNTER.next().to_string()) which isn't stable across launches — using that as the autosave key would actively break position persistence in apps that don't override the id. Opt-in keeps existing behaviour unchanged and lets callers supply a stable key intentionally.

Verification

• cargo check ✓
• cargo check --all-features ✓
• cargo clippy --all-targets ✓ (no new warnings)
• cargo test --no-run ✓
• Real app verification: built downstream against this patched copy, ⌘+drag persists across launchctl kickstart restarts on a 16" M2 Max MacBook Pro.

Changefile

Included .changes/macos-autosave-name.md (minor bump — additive API).

Reference

• Apple docs: NSStatusItem.autosaveName
• Same approach used by Bartender, Hidden Bar, etc.