feedback5 WI: UI strings through t() with an English switch on the title screen and in 设置; pilot screens converted

public/i18n/en.json: Chinese msgid -> English, seeded from PR #70 (@YuriRestia, credited) for every Chinese
literal of the current code (≈830 entries; 966 of the 1 036 literals left for phase 2 already translated),
completed by hand in the official EN terms. public/js/ui/lang.js: boot language (?lang=en|zh, then
localStorage sp.pref.lang, else Chinese; the browser language is not consulted), switchLang, useLang,
LangToggle; main.js renders after initLang and re-renders in place on a switch, and translates server
texts (m.toast / m.ticker frames, room.closed reasons, error codes via ui/toasts.js describeError).
Converted: title screen (English title, wordmark hidden), lobby, room, settings (语言 row, On/Off,
quality, hotkeys), the shell (crash screen, toasts) and DifficultyTag.

tools/i18n.mjs: extract (msgids + untranslated literals per file), check (msgids missing from en.json),
codemod (html`` text / attributes / strings / template literals -> t(), nested strings, N_ for module
level, i18n-ignore lines), seed (fill en.json from a msgid map).

public/css/screens/title.css

@@ -192,6 +192,8 @@
   animation: rise-in 600ms 140ms var(--ease-out) backwards;
 }
 .title-cn__colon { color: #f4f6f5; }
+/* English title (ui/lang.js): the display face, smaller so "Stronghold Protocol: Alliance" fits one line */
+.title-cn--latin { font-family: var(--font-display); font-size: .6rem; font-weight: 700; letter-spacing: .04em; text-transform: uppercase; white-space: nowrap; }
 .title-cn em { font-style: normal; color: var(--mint-500); text-shadow: 0 0 .26rem rgba(23, 249, 183, .45); }
 .title-tag {
   margin-top: .12rem;
@@ -241,6 +243,10 @@
 .title-invite .icon { width: .2rem; height: .2rem; }
 .title-invite b { font-size: .2rem; letter-spacing: .2em; color: #ffd08a; }
 .title-conn { display: flex; align-items: center; justify-content: center; gap: .1rem; min-height: .32rem; font-size: .14rem; color: var(--text-lo); }
+/* language switch (中文 | English) in the top-right corner */
+.title-lang { display: inline-flex; margin-bottom: .1rem; }
+.title-lang button { min-width: .74rem; height: .3rem; font-size: .14rem; cursor: pointer; }
+html[data-lang="en"] .title-login .btn--xl { letter-spacing: .3em; }
 .title-conn .ping { height: .26rem; font-size: .15rem; }
 
 .title-foot {