feat: add tray icon visibility toggle

[Mr-Sunglasses]

Summary

• Add a persisted General settings toggle to show or hide the VocaMac menu bar icon.
• Use MenuBarExtra's isInserted binding for runtime tray-item visibility.
• Keep Settings available through the standard macOS settings shortcut when the icon is hidden.
• Add toggle persistence tests and update documentation.

Validation

• swift build
• swift test: 306 tests passed, 3 skipped, 0 failures
• git diff --check

[Mr-Sunglasses]

Agreed with @jatinkrmalik, that we don't need this feature for now because vocamac is totally dependent on tray and when we make it visibility off then how can we access the settings in different aspect of app so closing this in a favor that we don't need it now.