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

backend/deploy/nginx-visual.loki-code.dev.conf

@@ -10,6 +10,10 @@ server {
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
         proxy_set_header X-Forwarded-Proto $scheme;
+        # The backend scopes the refresh cookie to Path=/auth, but the frontend calls it
+        # under /api/auth/* through this proxy — without this rewrite the browser never
+        # sends the cookie back on /api/auth/refresh and the session is lost on reload.
+        proxy_cookie_path /auth /api/auth;
     }
 
     location / {