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

OSGKeyboardExt/KeyboardViewController.swift

@@ -105,6 +105,12 @@ public final class KeyboardViewController: UIInputViewController {
         super.viewDidAppear(animated)
         disableSystemGestureDelays()
         keyboardHeightConstraint?.constant = targetKeyboardHeight
+        refreshReturnKeyRole()
+    }
+
+    public override func textDidChange(_ textInput: UITextInput?) {
+        super.textDidChange(textInput)
+        refreshReturnKeyRole()
     }
 
     public override var preferredScreenEdgesDeferringSystemGestures: UIRectEdge {
@@ -195,6 +201,21 @@ public final class KeyboardViewController: UIInputViewController {
         }
     }
 
+    private func refreshReturnKeyRole() {
+        state.returnKeyRole = returnKeyRole(for: textDocumentProxy.returnKeyType ?? .default)
+    }
+
+    private func returnKeyRole(for returnKeyType: UIReturnKeyType) -> State.ReturnKeyRole {
+        switch returnKeyType {
+        case .send, .go, .search, .join, .route, .google, .yahoo, .continue, .emergencyCall:
+            return .send
+        case .default, .next, .done:
+            return .newline
+        @unknown default:
+            return .newline
+        }
+    }
+
     // MARK: - System keyboard chrome
 
     private func configureDictationBehavior() {