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/Models/ProviderLogo.swift

@@ -0,0 +1,24 @@
+// ProviderLogo.swift
+// OSGKeyboard · Shared
+//
+// Maps a provider id to its asset-catalog logo name. Shared by the iOS
+// app and the macOS menu-bar app so both show identical brand marks.
+
+import Foundation
+
+public enum ProviderLogo {
+    /// Asset name for the provider's logo, or `nil` when there is no bundled logo.
+    public static func assetName(for providerId: String) -> String? {
+        switch providerId {
+        case "openai": return "openai"
+        case "deepseek": return "deepseek"
+        case "qwen": return "qwen"
+        case "moonshot": return "moonshot"
+        case "zhipu": return "zhipu"
+        case "mimo": return "mimo"
+        case "apple": return "apple"
+        case "custom": return "custom"
+        default: return nil
+        }
+    }
+}