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/AppGroupStore.swift

@@ -16,15 +16,25 @@ public struct AppGroupStore: @unchecked Sendable {
             self.defaults = defaults
             return
         }
-        guard let available = AppGroup.defaultsIfAvailable else {
-            #if DEBUG
-            fatalError("App Group unavailable — inject UserDefaults in tests or fix entitlements.")
-            #else
-            // Callers must check `AppGroup.isAvailable` before constructing.
-            fatalError("App Group unavailable.")
-            #endif
+        if let available = AppGroup.defaultsIfAvailable {
+            self.defaults = available
+            return
         }
-        self.defaults = available
+        #if os(iOS)
+        // iOS app + keyboard extension MUST share the App Group suite; a
+        // silent `.standard` fallback would desync them. Keep this a hard
+        // failure so a provisioning mistake is impossible to miss.
+        #if DEBUG
+        fatalError("App Group unavailable — inject UserDefaults in tests or fix entitlements.")
+        #else
+        fatalError("App Group unavailable.")
+        #endif
+        #else
+        // macOS is a standalone menu-bar app with no keyboard extension to
+        // stay in sync with, so a missing App Group container is expected;
+        // fall back to the app's standard defaults.
+        self.defaults = .standard
+        #endif
     }
 
     private var configuration: AppGroupConfiguration {
@@ -165,6 +175,14 @@ public struct AppGroupStore: @unchecked Sendable {
         AppGroupConfigDarwin.postConfigChanged()
     }
 
+    public func deletePersonalDictionaryEntry(id: UUID, at date: Date = Date()) {
+        mutateConfiguration { config in
+            config.personalDictionary.entries.removeAll { $0.id == id }
+            config.personalDictionary.deletedEntryIDs[id] = date
+        }
+        AppGroupConfigDarwin.postConfigChanged()
+    }
+
     public var personalDictionaryICloudSyncEnabled: Bool {
         get { configuration.personalDictionaryICloudSyncEnabled }
         set { setPersonalDictionaryICloudSyncEnabled(newValue) }