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/PersonalDictionaryCloudSync/PersonalDictionaryCloudSync.swift

@@ -24,7 +24,8 @@ public enum PersonalDictionaryCloudSyncError: Error, Equatable, Sendable {
 public final class PersonalDictionaryCloudSync {
     public static let shared = PersonalDictionaryCloudSync()
 
-    public static let kvsKey = "personalDictionary.v1"
+    public static let kvsKey = PersonalDictionary.kvsKeyV2
+    public static let legacyKVSKey = PersonalDictionary.legacyKVSKey
     /// Stay below the ~1 MB per-key KVS limit.
     public static let maxPayloadBytes = 900_000
 
@@ -124,8 +125,11 @@ public final class PersonalDictionaryCloudSync {
     }
 
     public func loadRemote() -> PersonalDictionary? {
-        guard let data = kvs.data(forKey: Self.kvsKey) else { return nil }
-        return try? decode(data)
+        if let data = kvs.data(forKey: Self.kvsKey) {
+            return try? decode(data)
+        }
+        guard let legacyData = kvs.data(forKey: Self.legacyKVSKey) else { return nil }
+        return try? decode(legacyData)
     }
 
     // MARK: - Encoding