fix(frontend): session cookie path, browser-language default, avatar crop, EN link previews, topbar logo

- nginx: rewrite the refresh cookie's Path=/auth to /api/auth on the
  production proxy — without this the browser never sent the cookie
  back on POST /api/auth/refresh and the session was lost on reload
- i18n: fallbackLng ru -> en, so only an actual ru browser locale
  defaults to Russian, everything else defaults to English
- index.html: explicit English og:*/twitter:* tags so link previews
  in Discord/etc. don't fall back to the (Russian) meta description
- Avatar upload: pick -> circular crop/reposition/zoom preview ->
  confirm -> upload, instead of uploading the raw file blind
- Topbar: logo pill background removed, pixel-heart mark added next
  to the LoVisual wordmark
- Fixed two tests left stale by the earlier tagline copy change

Claude-Session: https://claude.ai/code/session_01F1M1Jic1wTSn4igUENynmZ

frontend/src/app/i18n.ts

@@ -60,7 +60,9 @@ export function initI18n(lng?: 'ru' | 'en'): i18n {
           profile: profileEn,
         },
       },
-      fallbackLng: 'ru',
+      // Browser language decides the default: only an actual `ru` locale gets Russian,
+      // every other system language falls back to English.
+      fallbackLng: 'en',
       supportedLngs: ['ru', 'en'],
       ns: ['common', 'auth', 'landing', 'themes', 'clickgui', 'download', 'deviceLink', 'account', 'configs', 'showcase', 'profile'],
       defaultNS: 'common',