Add WalletConnect stub, track surfaces, legacy SPA retirement, and dual-domain checks.

Publish walletconnect config endpoints, Track 3/4 notes on analytics/operator pages, legacy SPA at /legacy/index.html with root redirect, and a parity verifier for explorer.d-bis.org vs blockscout.defi-oracle.io.

Co-authored-by: Cursor <cursoragent@cursor.com>

deployment/common/nginx-next-frontend-proxy.conf

@@ -12,6 +12,12 @@
 # Include these locations after those API/static locations and before any legacy
 # catch-all that serves /var/www/html/index.html directly.
 
+location ^~ /legacy/ {
+    alias /var/www/html/legacy/;
+    try_files $uri $uri/ /legacy/index.html;
+    add_header Cache-Control "no-store, no-cache, must-revalidate" always;
+}
+
 location ^~ /_next/ {
     proxy_pass http://127.0.0.1:3000;
     proxy_http_version 1.1;