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/zh-Hans.lproj/Keyboard.strings

@@ -210,6 +210,7 @@
 "keyboard.clipboard.guide.cta" = "去设置开启";
 "keyboard.clipboard.panel.title" = "剪贴板";
 "keyboard.clipboard.panel.empty" = "暂无历史记录";
+"keyboard.clipboard.panel.emptyHint" = "复制的文字会出现在这里。";
 "keyboard.clipboard.panel.fullAccessHint" = "「允许完全访问」已关闭，新复制内容将暂停采集，已有历史仍可使用。";
 "keyboard.clipboard.panel.delete" = "删除";
 "keyboard.clipboard.panel.close" = "关闭剪贴板";
@@ -370,6 +371,8 @@
 "keyboard.ai.skill.createContact" = "新建联系人";
 "keyboard.ai.skill.extractConclusions" = "提取结论";
 "keyboard.ai.skill.translate" = "翻译";
+"keyboard.ai.skill.translateToTarget" = "翻译";
+"keyboard.ai.skill.polishOriginal" = "优化";
 "keyboard.ai.skill.acceptInvitation" = "接受邀约";
 "keyboard.ai.skill.declineInvitation" = "委婉拒绝";
 "keyboard.ai.skill.acceptTask" = "确认任务";