* fix(linux): restore the macOS build of the Tauri companion
Tauri gates `WebviewWindowBuilder::transparent` behind its `macos-private-api`
feature on macOS, so the companion stopped compiling for macOS when Quick Chat
landed in #109947: `no method named 'transparent' found for struct
'WebviewWindowBuilder'`. Enable that feature together with the matching
`app.macOSPrivateApi` config flag, which Tauri requires to agree with it or
tauri-build fails the allowlist check.
Quick Chat is built for a transparent window - quickchat.css makes html and
body transparent behind a 16px-radius translucent card with a drop shadow - so
compiling macOS by dropping `.transparent(true)` would ship an opaque rectangle
instead of the floating composer.
Also add a per-PR macOS `cargo check`. The only job that compiled the macOS
target sits behind a manual dispatch input in linux-app-release.yml, which is
why a broken macOS build survived for nine days.
* ci(linux): build the macOS companion on macos-15
tauri-plugin-notifications' Swift sources use typed throws
(`throws(FFIResult)`), which requires Swift 6. The macos-14 runner image still
ships Swift 5.x and cannot parse them, so the plugin's build script panics with
"Swift build failed for target: arm64-apple-macosx13.0".
This hit the new per-PR check immediately, and it means the release workflow's
`build_macos` job could not have produced a macOS bundle either - it compiles
the same crate on the same image, but only runs behind a manual dispatch input
so nothing surfaced it. Move both to macos-15.
e94796e447