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

OSGKeyboardExt/Utilities/OSGHostArbiterProbe.m

@@ -1,13 +1,11 @@
 // OSGHostArbiterProbe.m
 // OSGKeyboard · Keyboard Extension
 //
-// 临时调试探针（仅 DEBUG），见头文件说明。所有私有符号都在运行时按字符串查找，
+// 宿主识别探针（所有构建配置均编译），见头文件说明。所有私有符号都在运行时按字符串查找，
 // 任何一步找不到都静默放弃，并保证原始实现照常执行。
 
 #import "OSGHostArbiterProbe.h"
 
-#ifdef DEBUG
-
 #import <UIKit/UIKit.h>
 #import <objc/message.h>
 #import <objc/runtime.h>
@@ -129,5 +127,3 @@ static BOOL OSGAlwaysEnabled(__unused id self, __unused SEL _cmd) {
 }
 
 @end
-
-#endif