Show the language model's opinion on a message

When inbuxa-server's AI spam classification is on, it records the model's
answer in an X-Spam-LLM header: a tag (LLM_<category>[_<confidence>]) and,
in parentheses, the model's explanation. The full message now asks for it,
and where it's there:

- the message details show "Language model's opinion" beside the spam
  filter's own working, with category, confidence and explanation;
- a message in Junk carries a banner saying the same.

Both say it's one of several signals the spam filter weighed, never the
reason on its own, as the server's spec requires. The explanation is model
output and is only ever rendered as text. Nothing shows without the header,
so a server without the feature, or with it off, looks as before.

Translations: two new strings, "Language model's opinion" and "One of
several signals the spam filter weighed", in all eight catalogues (16
entries). Category and confidence come from the server and aren't
translated.

web/src/locales/zh-Hans.ts

@@ -1720,6 +1720,9 @@ export const catalog: Catalog = {
     "To confirm, type {phrase}": "请输入 {phrase} 以确认",
     "Turn off legacy protocols": "关闭传统邮件协议",
     "Legacy mail protocols are off for your organization. Only {app} and JMAP apps can sign in.": "您的组织已关闭传统邮件协议。只有 {app} 和 JMAP 应用可以登录。",
+    // ── Spam filter: the language model's opinion (inbuxa) ──────────
+    "Language model's opinion": "语言模型的判断",
+    "One of several signals the spam filter weighed": "垃圾邮件过滤考虑的多个信号之一",
   },
   plurals: {
     // ── Administration: legacy mail protocols (INBUXA) ──────────────