feat(macos): add macOS menu-bar app and harden cross-device iCloud sync

Introduce a standalone macOS menu-bar app (OSGKeyboardMac) that reuses the
platform-agnostic OSGKeyboardShared core: record -> cloud/local ASR -> polish
-> insert. Local mode uses Qwen3-ASR via mlx-swift-asr (macOS 15+, Apple
Silicon); iOS targets stay zero-SPM.

Harden iCloud sync for multi-device correctness:
- Per-field settings merge (appSettings.v2) so concurrent edits no longer
  clobber each other's unrelated fields.
- Per-device usage statistics (G-Counter) that sum instead of max().
- Tombstoned dictionary/history merge so deletes propagate and entries can't
  resurrect.
- API keys replicate via iCloud Keychain, never iCloud KVS JSON; pulling a
  legacy blob without key fields no longer wipes local Keychain entries.
- Add a low-risk "Sync Now" action in Settings.

Fix Flow keyboard mic state: stay orange until the host publishes a real ready
contract, share a single MicVoiceAvailability gate, and self-heal stale
cross-process heartbeat jitter instead of getting stuck.

Extract shared storage (SpeechHistoryStore/UsageStatisticsStore,
ConfigurationStore) into OSGKeyboardShared and add tests for the new
sync/merge logic.

OSGKeyboardShared/Services/CloudASR/CloudASRService.swift

@@ -8,7 +8,7 @@ import Foundation
 import os
 
 public final class CloudASRService: ASRService, @unchecked Sendable {
-    private let store: AppGroupStore
+    private let store: any ConfigurationStore
     private let session: URLSession
     private let localFallback: ASRService
     private let lock = OSAllocatedUnfairLock()
@@ -18,7 +18,7 @@ public final class CloudASRService: ASRService, @unchecked Sendable {
     private var cancelled = false
 
     public init(
-        store: AppGroupStore = AppGroupStore(),
+        store: any ConfigurationStore = AppGroupStore(),
         session: URLSession = .shared,
         localFallback: ASRService? = nil
     ) {