chore(release): bump version to 2.1.6 (build 131)

Version: CURRENT_PROJECT_VERSION 130 -> 131 (project.yml, AGENTS.md, READMEs,
docs/llms.txt).

fix(flow): host-app identification now compiles in every build configuration
(Debug, TestFlight, Release). The arbiter probe and HostAppIdentity were
DEBUG-only, so TestFlight/App Store builds never knew the host bundle id and
could not auto-return after a startflow handoff. Debug-only logging and the
Home test card are unchanged.

Also includes the pending work in the tree:
- Home: single account/setup card surface (HomeAccountSurfacePolicy/Views)
- Wide screens: voice key row and centred mic placement, iPhone Duo layout
- Keyboard: clipboard skill ranking and AI skill layout updates
- Debug: account session handoff to the Simulator (+ import script)
- Docs: portfolio assets, privacy policy URL, site/README refresh

project.yml

@@ -48,8 +48,8 @@ settings:
     ASSETCATALOG_COMPILER_GENERATE_SWIFT_ASSET_SYMBOL_EXTENSIONS: YES
     STRING_CATALOG_GENERATE_SYMBOLS: YES
     CLANG_CXX_LANGUAGE_STANDARD: c++17
-    MARKETING_VERSION: "2.1.5"
-    CURRENT_PROJECT_VERSION: "125"
+    MARKETING_VERSION: "2.1.6"
+    CURRENT_PROJECT_VERSION: "131"
     # 签名配置来自 Signing.local.xcconfig（gitignored，不会被覆盖）
 
 # 项目级签名 xcconfig，适用于所有 target
@@ -598,6 +598,7 @@ targets:
       - path: OSGKeyboard/Views/Account/AccountCreditStore.swift
       - path: OSGKeyboard/Views/Account/AccountCreditPurchaseManager.swift
       - path: OSGKeyboard/Views/Account/LiveAccountServices.swift
+      - path: OSGKeyboard/Views/Account/DebugAccountSessionHandoff.swift
       - path: OSGKeyboard/Views/Account/ReferralProfileViewModel.swift
       # Invitation QR poster: pure SwiftUI + Core Image, shared with iOS.
       - path: OSGKeyboard/Views/Account/InvitePoster.swift