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).

OSGKeyboardShared/Services/LocalASRPreferenceKeys.swift

@@ -0,0 +1,8 @@
+// LocalASRPreferenceKeys.swift
+// OSGKeyboard · Shared
+
+import Foundation
+
+enum LocalASRPreferenceKeys {
+    static let selectedModelId = "mac.localASR.selectedModelId"
+}