web: share the landing page to social networks with a real preview card

Open Graph and Twitter Card meta point at a 1200x630 cover shot of the
hero, and the final CTA grows a share row: Facebook, X, LinkedIn and
Telegram each open with this origin filled in, plus a native share sheet
that falls back to copying the link. The top bar now leads with the web
studio pill next to the store CTA, with the theme, language and account
controls trailing them.

docker/frontend/src/styles/landing.css

@@ -424,6 +424,9 @@ html { scroll-behavior: smooth; scroll-padding-top: 78px; }
 .lp-store { display: flex; flex-direction: column; align-items: flex-start; line-height: 1.25; }
 .lp-store small { font-family: var(--lp-mono); font-size: 9.5px; color: var(--lp-muted); }
 .lp-store b { font-size: 15px; }
+/* Share row under the store badges: the label reads as a mono caption. */
+.lp-share { display: flex; align-items: center; justify-content: center; gap: 10px; flex-wrap: wrap; margin-top: 26px; }
+.lp-share-label { font-family: var(--lp-mono); font-size: 10px; letter-spacing: 0.12em; color: var(--lp-muted); margin-right: 4px; }
 .lp-footer { border-top: 1px solid var(--lp-line); padding: 30px 0 40px; }
 .lp-footer .lp-wrap { display: flex; flex-wrap: wrap; gap: 14px 26px; align-items: center; font-size: 12.5px; color: var(--lp-muted); }
 .lp-footer a:hover { color: var(--lp-text); }