feat: macOS architecture, cloud ASR/LLM providers, and 6-step iOS onboarding

- Add macOS menu-bar dictation app with local ASR models (SenseVoice/Qwen3),
  global Option hotkey, and bottom overlay
- Add cloud ASR/LLM providers (Anthropic, Volcengine, Bailian, and more) with
  provider logos, model listing, and connection checks
- Add shared 7-day usage stats UI (UsageStatsCluster / SevenDayUsageChart)
- Add iOS onboarding step 6 for polish LLM setup; hide custom-language-model
  diagnostic toggle behind DEBUG
- Unify iOS onboarding tagline with the macOS brand line ("开口即文字。")
- Rewrite README (Chinese-first, product-oriented) and refresh GitHub Pages

OSGKeyboardShared/Services/CloudASR/CloudASRConnectionCheck.swift

@@ -0,0 +1,19 @@
+// CloudASRConnectionCheck.swift
+// OSGKeyboard · Shared
+//
+// Settings "validate connection" probe shared by iOS and macOS.
+
+import Foundation
+
+public enum CloudASRConnectionCheck {
+    /// Verifies the active cloud ASR client can connect + authenticate.
+    ///
+    /// Each backend decides how to probe (see `CloudASRTranscribing`):
+    /// HTTP/batch providers transcribe a short silence clip and treat an
+    /// empty transcript as success; DashScope realtime only handshakes to
+    /// `task-started` (pushing fake audio makes it fail with `emptyAudio`).
+    public static func validate(store: any ConfigurationStore) async throws {
+        let client = CloudASRClientFactory.make(store: store)
+        try await client.probeConnection()
+    }
+}