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/features/landing/tests/landing.test.tsx

@@ -37,5 +37,5 @@ test('english locale renders the landing hero headline', async () => {
       </QueryClientProvider>
     </I18nextProvider>,
   )
-  expect(await screen.findByRole('heading', { level: 1 })).toHaveTextContent('you can see')
+  expect(await screen.findByRole('heading', { level: 1 })).toHaveTextContent("you'll fall in love with")
 })