docs: 文档改为英文，并修正过时内容

不是翻译 —— 多数文档描述的行为已经不存在了。

先修一个更基本的问题：我们不拥有 u-claw.org 域名，那是上游的。所以之前写在
README、诊断包提示、联系方式里的 help@u-claw.org 全都会把用户的问题发给
上游 —— 一个没有理由回复的人。改为指向我们自己的 issue tracker，并加断言
禁止再出现指向该域名的支持入口。

重写（内容过时，不是语言问题）：
- install/README.md —— 还写着 10 个中国技能、DeepSeek 优先、国内镜像。
  现在按实际流程写：技能读 manifest、模型菜单 Gemini 优先、bundle 有
  SHA256 校验。并如实写明 curl|bash 在受管企业电脑上会被 EDR 拦。
- CLAUDE.md 的模型配置整节 —— 还在描述虾盘云首选卡片和 12 个 provider，
  那个界面已经换成单框 Key 输入了。
- SECURITY.md —— 安全报告原本指向上游维护者个人邮箱。fork 之后那条路由
  是错的：漏洞会发给写不了这份代码、也修不了的人。
- CONTRIBUTING.md —— 补上 fork 关系、pre-push 钩子怎么装、以及
  `node --test tests/` 为什么不能用。

翻译并保留：
- bootable/README.md、TROUBLESHOOTING.md —— 面向用户，顺带把
  「国内镜像」「小米/华为 BIOS 按键」等换成目标市场的实际情况

HANDOFF.md 重写为一份事故复盘：原文一半是过时的一次性交接笔记（引用的
website/guide.html 已不在本仓库），另一半是 persistence.dat 未格式化导致
启动失败的排查记录 —— 后者有长期价值，尤其是「读 offset 1080 的两字节
验证 ext4」这个判断方法，已同时写进 bootable/README.md。

bootable/IMPROVEMENTS_SUMMARY.md 保留中文，加了说明：它是上游 fork 前的
历史改进记录，没人引用，描述的是已完成的工作而非当前行为。翻译它反而会
让人误以为是现行文档。

新增 skills/en/uclaw-help —— 把「怎么用、东西在哪、出问题怎么办」做成
内置知识，每个角色都装。方案 C10.8：能问的产品才是不需要学的产品。

portable/lib/i18n/messages.js

@@ -230,7 +230,7 @@ window.UCLAW_I18N_MESSAGES = {
     "start.checking": "Something went wrong — checking…",
     "start.repaired": "Fixed. Trying again.",
     "start.diagnostics_written": "A report of what happened was saved to: {path}",
-    "start.diagnostics_hint": "API keys have been removed from it. Send it to help@u-claw.org if you want a hand.",
+    "start.diagnostics_hint": "API keys have been removed from it. Attach it to an issue at https://gitea.fanghe.it.com/zhenghy/u-claw/issues if you want a hand.",
     "skill.excel-helper.name": "Spreadsheets",
     "skill.excel-helper.desc": "Formulas, pivot tables, charts, cleaning messy data",
     "skill.word-writer.name": "Documents",
@@ -282,7 +282,11 @@ window.UCLAW_I18N_MESSAGES = {
     "hub.lede": "These are on this drive already. Just ask for what you want — you do not have to name the skill.",
     "hub.all": "All",
     "hub.none": "Nothing in this category.",
-    "hub.add_note": "Skills live in the skills/ folder on this drive. Dropping a SKILL.md in there adds one."
+    "hub.add_note": "Skills live in the skills/ folder on this drive. Dropping a SKILL.md in there adds one.",
+    "nav.link_contact_d": "Open an issue",
+    "skill.uclaw-help.name": "About U-Claw",
+    "skill.uclaw-help.desc": "How it works, where things are, what to do when something breaks",
+    "cat.uclaw": "U-Claw"
   },
   "zh-CN": {
     "start.banner": "U-Claw · 便携 AI 助手",
@@ -509,7 +513,7 @@ window.UCLAW_I18N_MESSAGES = {
     "start.checking": "出了点问题，正在检查…",
     "start.repaired": "已修复，重试一次。",
     "start.diagnostics_written": "已把情况记录到：{path}",
-    "start.diagnostics_hint": "里面的密钥已被去掉。需要帮忙的话，把它发到 help@u-claw.org。",
+    "start.diagnostics_hint": "里面的密钥已被去掉。需要帮忙的话，把它附到 https://gitea.fanghe.it.com/zhenghy/u-claw/issues 的 issue 里。",
     "skill.excel-helper.name": "表格",
     "skill.excel-helper.desc": "公式、透视表、图表、清洗乱数据",
     "skill.word-writer.name": "文档",
@@ -561,6 +565,10 @@ window.UCLAW_I18N_MESSAGES = {
     "hub.lede": "这些已经在盘上了。直接说你想做什么就行，不用记技能名。",
     "hub.all": "全部",
     "hub.none": "这个分类下暂时没有。",
-    "hub.add_note": "技能放在盘上的 skills/ 目录里。丢一个 SKILL.md 进去就多一个。"
+    "hub.add_note": "技能放在盘上的 skills/ 目录里。丢一个 SKILL.md 进去就多一个。",
+    "nav.link_contact_d": "提 issue",
+    "skill.uclaw-help.name": "关于 U-Claw",
+    "skill.uclaw-help.desc": "它怎么用、东西在哪、出问题了怎么办",
+    "cat.uclaw": "U-Claw"
   }
 };

portable/lib/i18n/skills-data.js

@@ -48,6 +48,22 @@ window.UCLAW_SKILLS = {
     }
   ],
   "skills": [
+    {
+      "id": "uclaw-help",
+      "categories": [
+        "uclaw"
+      ],
+      "personas": [
+        "developer",
+        "admin",
+        "sales",
+        "marketing",
+        "finance",
+        "boss",
+        "general"
+      ],
+      "emoji": "🦞"
+    },
     {
       "id": "excel-helper",
       "categories": [