feat(insights): 箱主数据面板——访问量、提问趋势、处理漏斗

新增 /user/insights，让箱主第一次能看到「有多少人来过我的箱、提问处理得怎么样」。

数据来源：
- 新表 box_views：一行 = 一访客×一天×一箱，views 累加，唯一索引
  (user_id, viewed_on, visitor)。刻意不内嵌 dbutil.Model —— 软删除 + 唯一索引
  会让被删行永久占槽，且删过的槽位再也插不进去。
- 访客标识 = HMAC(日盐, IP) 前 32 hex：同日可去重（UV 准）、跨日不可关联（隐私）。
  代价是近 7/30 天 UV = 各日 UV 之和，页面上已写明口径。

写入是异步的：buffered channel 512 + 2s 批量 flush，队列满即丢（统计尽力而为，
不该因为记一笔访问就拖慢页面）。过滤箱主本人、空 UA、爬虫 UA、预取请求。
密钥复用 server.xsrf_key；每日清理 400 天前的明细。

页面（纯 CSS 画图，不引图表库）：
- 今日/近 7 天/近 30 天 KPI + 上周对比
- 30 天 PV/UV 双柱趋势、24 小时时段分布
- 提问处理漏斗 + 回答率进度条 + 自动结论

聚合层 internal/db/box_analytics.go 复用 analyticsDialectFor 的时区处理，
与全站 stats 分开（那个不含单箱维度、按自然日缓存）。

测试：box_views 4 项（含「同批同键先内存合并」——PG 的 ON CONFLICT 不允许
同条 INSERT 二次命中同一行）、insights 的 pct/窗口切分/visitorID/爬虫过滤。

internal/i18n/dict_en.go

@@ -1054,6 +1054,50 @@ var enDict = map[string]string{
 	"stats.weekday.6": "Saturday",
 	"stats.weekday.7": "Sunday",
 
+	// Owner insights panel (/user/insights)
+	"insights.title":        "Insights",
+	"insights.heading":      "Your insights",
+	"insights.lead":         "These numbers are yours alone: how many people opened your box, how many questions arrived, and how many are still waiting. Everything is aggregated — no visitor or asker is ever identified.",
+	"insights.back":         "Back to settings",
+	"insights.entryTitle":   "Insights",
+	"insights.entryDesc":    "See how many people visit your box and how your questions are doing",
+	"insights.summary":      "At a glance",
+	"insights.noViews":      "No visits recorded yet. Numbers will appear once someone opens your box.",
+	"insights.today":        "Today",
+	"insights.week":         "Last 7 days",
+	"insights.month":        "Last 30 days",
+	"insights.newQuestions": "new questions",
+	"insights.pv":           "views",
+	"insights.uv":           "visitors",
+	"insights.trendTitle":   "Views over the last 30 days",
+	"insights.trendNote":    "One bar per day: the light part is page views, the dark part is unique visitors that day. Hover a bar for its views / visitors / questions.",
+	"insights.legendPV":     "Page views",
+	"insights.legendUV":     "Unique visitors (per day)",
+	"insights.legendHover":  "Hover for daily details",
+	"insights.hourTitle":    "When people show up",
+	"insights.hourNote":     "When questions arrived during the last 30 days. The brightest bar is your busiest hour.",
+	"insights.funnelTitle":  "Question handling",
+	"insights.funnelNote":   "All questions split into answered / read but unanswered / untouched.",
+	"insights.funnelTotal":    "All questions",
+	"insights.funnelAnswered": "Answered",
+	"insights.funnelReadOnly": "Read, not answered",
+	"insights.funnelUnread":   "Not read",
+	"insights.answerRate":   "Answer rate: answered ÷ all questions",
+	"insights.privacyTitle": "About these numbers",
+	"insights.privacyNote":  "Visit stats only record \"someone visited N times on a given day\". A visitor is an IP hash with a per-day salt — no IP, no user agent, no page path is stored, and the same person cannot be linked across days. The 7-day / 30-day visitor counts are therefore the sum of daily uniques: someone visiting on several days counts several times. Your own visits to your own box are excluded.",
+
+	"insights.insight.empty":      "No data yet. This page comes alive once you get your first question or someone opens your box.",
+	"insights.insight.weekViews":  "%s views from %s visitors in the last 7 days.",
+	"insights.insight.conversion": "About %s%% of visitors left a message in the last 30 days.",
+	"insights.insight.bestDay":    "Your busiest day was %s with %s views.",
+	"insights.insight.peakHour":   "Questions cluster around %d:00.",
+	"insights.insight.answerRate": "You have answered %s%% of all questions.",
+	"insights.insight.fastReply":  "%s%% of your answers went out within 24 hours.",
+	"insights.insight.unread":     "%s questions are still waiting.",
+	"insights.insight.trendUp":    "Views this week are up %s%% on last week.",
+	"insights.insight.trendDown":  "Views this week are down %s%% on last week.",
+	"insights.insight.trendFlat":  "Views this week are about the same as last week.",
+
 	"stats.foot.updated":    "Snapshot:",
 	"stats.foot.prevMonth":  "Last question:",
 	"stats.foot.prevAnswer": "Last answer:",