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

OSGKeyboardTests/AppGroupConfigurationTests.swift

@@ -17,7 +17,8 @@ final class AppGroupConfigurationTests: XCTestCase {
         let defaults = makeDefaults()
         let config = AppGroupConfiguration.load(fromAvailable: defaults)
 
-        XCTAssertEqual(config.providerId, "openai")
+        XCTAssertEqual(config.providerId, "deepseek")
+        XCTAssertEqual(config.asrProviderId, "volcengine")
         XCTAssertEqual(config.modeId, "polish")
         XCTAssertEqual(config.localeId, "auto")
         // Privacy-critical: the default engine must keep audio on-device.
@@ -125,14 +126,14 @@ final class AppGroupConfigurationTests: XCTestCase {
         XCTAssertFalse(config.translationEnabled)
     }
 
-    func testCloudDeepSeekProviderMigratesToOpenAI() {
+    func testCloudDeepSeekProviderIsPreserved() {
         let defaults = makeDefaults()
         defaults.set("deepseek", forKey: AppGroupConfiguration.Keys.providerId)
         defaults.set("cloud", forKey: AppGroupConfiguration.Keys.engineMode)
 
         let config = AppGroupConfiguration.load(fromAvailable: defaults)
-        XCTAssertEqual(config.providerId, "openai")
-        XCTAssertEqual(defaults.string(forKey: AppGroupConfiguration.Keys.providerId), "openai")
+        XCTAssertEqual(config.providerId, "deepseek")
+        XCTAssertEqual(defaults.string(forKey: AppGroupConfiguration.Keys.providerId), "deepseek")
     }
 
     func testPolishIntensityLegacyOffMigratesToMedium() {