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/uk.ts

@@ -1709,6 +1709,9 @@ export const catalog: Catalog = {
     "To confirm, type {phrase}": "Для підтвердження введіть {phrase}",
     "Turn off legacy protocols": "Вимкнути застарілі поштові протоколи",
     "Legacy mail protocols are off for your organization. Only {app} and JMAP apps can sign in.": "Застарілі поштові протоколи вимкнено для вашої організації. Входити можуть лише {app} і програми JMAP.",
+    // ── Spam filter: the language model's opinion (inbuxa) ──────────
+    "Language model's opinion": "Думка мовної моделі",
+    "One of several signals the spam filter weighed": "Одна з кількох ознак, які врахував спам-фільтр",
   },
   plurals: {
     // ── Administration: legacy mail protocols (INBUXA) ──────────────