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/LocalASRInstalledManifestIO.swift

@@ -0,0 +1,32 @@
+// LocalASRInstalledManifestIO.swift
+// OSGKeyboard · Shared
+
+import Foundation
+
+public enum LocalASRInstalledManifestIO {
+
+    public static func manifestURL(fileManager: FileManager = .default) -> URL {
+        let appSupport = fileManager.urls(for: .applicationSupportDirectory, in: .userDomainMask).first!
+        return appSupport
+            .appendingPathComponent("OSGKeyboard/LocalASRModels/installed-manifest.json")
+    }
+
+    public static func load(defaultModelId: String, fileManager: FileManager = .default) -> LocalASRInstalledManifest {
+        let url = manifestURL(fileManager: fileManager)
+        guard let data = try? Data(contentsOf: url),
+              let manifest = try? JSONDecoder().decode(LocalASRInstalledManifest.self, from: data) else {
+            return LocalASRInstalledManifest(selectedModelId: defaultModelId)
+        }
+        return manifest
+    }
+
+    public static func save(_ manifest: LocalASRInstalledManifest, fileManager: FileManager = .default) throws {
+        let url = manifestURL(fileManager: fileManager)
+        try fileManager.createDirectory(at: url.deletingLastPathComponent(), withIntermediateDirectories: true)
+        let encoder = JSONEncoder()
+        encoder.outputFormatting = [.prettyPrinted, .sortedKeys]
+        encoder.dateEncodingStrategy = .iso8601
+        let data = try encoder.encode(manifest)
+        try data.write(to: url, options: .atomic)
+    }
+}