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.

OSGKeyboardMac/MacTextInsertionService.swift

@@ -0,0 +1,61 @@
+// MacTextInsertionService.swift
+// OSGKeyboard · Mac
+//
+// Inserts transcribed text into the frontmost app: clipboard first, then
+// a synthetic ⌘V (SayIt / Typeless-style). Requires Accessibility trust.
+
+import AppKit
+@preconcurrency import ApplicationServices
+import Carbon
+import Foundation
+
+enum MacTextInsertionService {
+    enum InsertionError: Error, LocalizedError {
+        case accessibilityNotGranted
+
+        var errorDescription: String? {
+            MacL10n.string("mac.error.accessibilityRequired")
+        }
+    }
+
+    static var isAccessibilityTrusted: Bool {
+        AXIsProcessTrusted()
+    }
+
+    @discardableResult
+    static func requestAccessibilityIfNeeded() -> Bool {
+        if AXIsProcessTrusted() { return true }
+        let promptKey = kAXTrustedCheckOptionPrompt.takeUnretainedValue() as String
+        let options = [promptKey: true] as CFDictionary
+        return AXIsProcessTrustedWithOptions(options)
+    }
+
+    /// Copy to pasteboard and optionally simulate ⌘V in the front app.
+    static func insert(
+        _ text: String,
+        autoPaste: Bool
+    ) throws -> Bool {
+        guard !text.isEmpty else { return false }
+        let pasteboard = NSPasteboard.general
+        pasteboard.clearContents()
+        pasteboard.setString(text, forType: .string)
+
+        guard autoPaste else { return false }
+        guard AXIsProcessTrusted() else { throw InsertionError.accessibilityNotGranted }
+
+        Thread.sleep(forTimeInterval: 0.08)
+        postCommandV()
+        return true
+    }
+
+    private static func postCommandV() {
+        let source = CGEventSource(stateID: .combinedSessionState)
+        let keyCode = CGKeyCode(kVK_ANSI_V)
+        let keyDown = CGEvent(keyboardEventSource: source, virtualKey: keyCode, keyDown: true)
+        let keyUp = CGEvent(keyboardEventSource: source, virtualKey: keyCode, keyDown: false)
+        keyDown?.flags = CGEventFlags.maskCommand
+        keyUp?.flags = CGEventFlags.maskCommand
+        keyDown?.post(tap: CGEventTapLocation.cghidEventTap)
+        keyUp?.post(tap: CGEventTapLocation.cghidEventTap)
+    }
+}