feat(macos): local ASR model manager, menu-bar polish, and release 0.5.2

Adds a bundled local ASR model catalog for the macOS app with one-click
Sherpa Qwen3 / SenseVoice downloads (pause/resume, inline actions) and a
shared model storage directory used by MLX Qwen3. Fixes the light-mode
sidebar material and makes the menu-bar icon follow the system appearance
with a refreshed status mark. Renames the built product to OSGKeyboard.app.

Bumps version to 0.5.2 (build 19).

OSGKeyboardMac/MacRootView.swift

@@ -56,7 +56,6 @@ struct MacRootView: View {
             Spacer()
             devicesFooter
         }
-        .background(palette.surfaceMuted)
     }
 
     private func sidebarRow(_ section: MacSection) -> some View {