feat(ux): 真 404 / HTML 500 页，以及「提问者找回自己的提问」

一、错误页

原来未知路径一律 302 到首页：用户点了个失效链接，地址栏莫名跳到首页却什么
提示都没有，分不清是链接坏了还是自己点错了；对搜索引擎是软 404，失效链接会
被当成有效页面一直占抓取预算。500 则是 flamego.Recovery() 的纯文本
"Internal Server Error"，白底黑字两行英文，没有返回入口，也没法报编号。

现在是 internal/route/errorpage.go 里的 writeErrorPage：
- 404 保留状态码 + 一页能看懂的说明 + 返回首页按钮 + noindex
- panic 由自写的 recoveryMiddleware 兜住，渲染同样的 HTML 500 页，
  并带上 trace id（用户反馈时报这个号就能定位日志），日志里也带完整栈
- 响应已写出时不再写头（否则 net/http 会忽略状态码并打 superfluous 警告）

为什么不套模板：f.NotFound 不经过组级中间件 —— template.Templater 与
Contexter（连同 session、CSRF）都挂在 f.Group 上，在 NotFound 里注入
template.Data 会直接 panic（实测："value not found for type template.Data"）。
而 recovery 是最外层，那时模板还没装配。错误页恰恰最不该依赖可能出错的链路，
所以用内联 HTML + i18n.T，语言从 Accept-Language 猜（拿不到 session）。

蜜罐分流仍在 NotFound 最前面：临时打开 enable_honeypot 实测 /wp-admin
仍返回假 WordPress 登录页（200），普通未知路径返回 404。

二、提问者找回自己的提问

不填邮箱时，唯一能追踪这条提问的东西是提问成功页上那条链接 —— 关掉页面、
链接冲掉了就永久失联。箱主认真答了，提问者永远不知道。这是这类产品最核心的
体验断点，而它不需要账号体系就能解决：

- 成功页把 {domain, id, token} 写进本机 localStorage（最多 30 条，按 domain+id 去重）
- 再访该箱时显示一条不打扰的横条：「这台设备上有 N 条提问记录，其中 M 条已有回答」，
  点「查看」展开列表，每条可直接打开
- 新增 POST /api/v1/ask-status 批量回答「哪些已被回答」：一次 IN 查询，不逐条 N+1

它不能用来枚举：必须同时给出正确 token 才返回 ok=true，而「token 错」「id 不存在」
「不属于该箱主」三种情况的响应完全相同（ok=false / answered=false / excerpt 为空），
无法区分。token 比较走常数时间，单次最多 20 条，限流 30/分钟。用 POST 不用 GET，
因为 token 不能进 URL（会留在浏览器历史、代理日志、Referer 里）。

列表摘要先过 MarkdownPlainText 再按 rune 截断：直接截原文会露出 ![图片](https://...)
这种噪音，一条带图的提问几乎只剩链接。

验证：
- verify_ask_history.py 12/12（含「错误 token / 不存在的 id / 别人的提问」三者
  响应完全一致、缺 CSRF 被拒、超 20 条截断）
- verify_ask_history_ui.mjs 用 CDP 在真实 Chrome 里跑：无记录时提示条隐藏；
  注入记录后显示「1 条，其中 1 条已有回答」；列表渲染、链接带 token、点击展开正常
- 错误页单测 6 项（HTML/不泄露 panic 内容/已写出时不重复写头/语言选择/状态码/转义）

internal/i18n/dict_en.go

@@ -88,41 +88,49 @@ var enDict = map[string]string{
 	"explore.noVotes":      "There are no public polls available right now.",
 
 	// Ask page
-	"ask.scan":              "Scan to ask @%s",
-	"ask.anonymous":         "Anyone can ask anonymously",
-	"ask.registerOnly":      "Only registered users can ask",
-	"ask.nextOpenAt":        "Next opening: %s",
-	"ask.lastCloseAt":       "Last closed: %s",
-	"weekday.0":             "Sun",
-	"weekday.1":             "Mon",
-	"weekday.2":             "Tue",
-	"weekday.3":             "Wed",
-	"weekday.4":             "Thu",
-	"weekday.5":             "Fri",
-	"weekday.6":             "Sat",
-	"ask.pinned":            "Pinned",
-	"ask.share":             "Share this box",
-	"ask.placeholder":       "Write your question here...",
-	"ask.chatPlaceholder":   "Write your chat message here...",
-	"ask.addImage":          "Add image",
-	"ask.private":           "Don't publish after reply",
-	"ask.notify":            "Notify me",
-	"ask.emailPlaceholder":  "Enter your email address",
-	"ask.submit":            "Send question",
-	"ask.chat":              "Start a chat",
-	"ask.chatDisabled":      "Chat is disabled on this box",
-	"ask.chatLimit":         "Message limit: %d",
-	"ask.history":           "Previously answered by @%s",
-	"ask.loginRequired":     "Log in required",
-	"ask.loginRequiredChat": "You need to log in to start a chat",
-	"ask.goLogin":           "Go to login",
-	"ask.needPassword":      "This box requires a password",
-	"ask.needLogin":         "The owner only allows registered users to ask questions. Please log in first.",
-	"ask.pleaseEmail":       "Please enter your email to receive notifications",
-	"ask.generating":        "Generating share card…",
-	"ask.genFailed":         "Failed to generate share card. Please try again later",
-	"ask.networkError":      "Network error",
-	"ask.shareFilename":     "share.png",
+	"ask.scan":                  "Scan to ask @%s",
+	"ask.anonymous":             "Anyone can ask anonymously",
+	"ask.registerOnly":          "Only registered users can ask",
+	"ask.nextOpenAt":            "Next opening: %s",
+	"ask.lastCloseAt":           "Last closed: %s",
+	"weekday.0":                 "Sun",
+	"weekday.1":                 "Mon",
+	"weekday.2":                 "Tue",
+	"weekday.3":                 "Wed",
+	"weekday.4":                 "Thu",
+	"weekday.5":                 "Fri",
+	"weekday.6":                 "Sat",
+	"ask.pinned":                "Pinned",
+	"ask.share":                 "Share this box",
+	"ask.placeholder":           "Write your question here...",
+	"ask.chatPlaceholder":       "Write your chat message here...",
+	"ask.addImage":              "Add image",
+	"ask.private":               "Don't publish after reply",
+	"ask.notify":                "Notify me",
+	"ask.emailPlaceholder":      "Enter your email address",
+	"ask.submit":                "Send question",
+	"ask.chat":                  "Start a chat",
+	"ask.chatDisabled":          "Chat is disabled on this box",
+	"ask.chatLimit":             "Message limit: %d",
+	"ask.history":               "Previously answered by @%s",
+	"askHistory.banner":         "You have {n} question(s) saved on this device",
+	"askHistory.answeredSuffix": ", {m} of them answered",
+	"askHistory.expand":         "View",
+	"askHistory.collapse":       "Hide",
+	"askHistory.answered":       "Answered",
+	"askHistory.pending":        "Awaiting reply",
+	"askHistory.open":           "Open",
+	"askHistory.note":           "Saved only in this browser. Switching devices or clearing browser data will lose them.",
+	"ask.loginRequired":         "Log in required",
+	"ask.loginRequiredChat":     "You need to log in to start a chat",
+	"ask.goLogin":               "Go to login",
+	"ask.needPassword":          "This box requires a password",
+	"ask.needLogin":             "The owner only allows registered users to ask questions. Please log in first.",
+	"ask.pleaseEmail":           "Please enter your email to receive notifications",
+	"ask.generating":            "Generating share card…",
+	"ask.genFailed":             "Failed to generate share card. Please try again later",
+	"ask.networkError":          "Network error",
+	"ask.shareFilename":         "share.png",
 
 	// Question item
 	"qitem.answer":            "Answer",
@@ -846,6 +854,7 @@ var enDict = map[string]string{
 	"vote.err.editClosed":                "Votes that are ended or archived cannot be edited",
 	"vote.err.publishDraftOnly":          "Only draft polls can be published",
 	"vote.err.restrictedPublish":         "Publishing is suspended while this account is under moderation",
+	"feature.stateUnavailable":           "Unable to verify the status of this feature, please try again later",
 	"vote.err.closePublishedOnly":        "Only active polls can be closed",
 	"vote.err.publishTitleRequired":      "Please fill in the poll title before publishing",
 	"vote.err.publishFormFieldsRequired": "Form polls need at least 1 field",
@@ -911,6 +920,12 @@ var enDict = map[string]string{
 	"chat.flash.operated":     "Operation successful",
 	"image.errTooLarge":       "Image is too large, maximum supported size is %d×%d pixels, please compress and re-upload",
 	"internal.errFlash":       "Internal server error, please try again later.",
+	"internal.errBadRequest":  "Invalid request",
+	"error.notFoundTitle":     "Page not found",
+	"error.notFoundDesc":      "There is nothing at this address. The link may be mistyped, or the content has been removed.",
+	"error.internalTitle":     "Something went wrong",
+	"error.internalDesc":      "This request could not be completed. It is usually temporary — try again in a moment.",
+	"error.traceHint":         "Please include this ID when reporting:",
 	"internal.errServer":      "Internal server error",
 	"home.errStats":           "Failed to retrieve statistics",
 	"pixel.errPath":           "Invalid request path",