fix: never cache HTML shell (no more stale bundles); tidy trick offsets

- nginx: serve the HTML shell with Cache-Control no-store so a new deploy (new
  chunk hashes) is picked up immediately — fixes the recurring stale-bundle
  "page couldn't load" at the source. Hashed /_next/static stays immutable.
- Trick offsets set to a clean symmetric cross.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

nginx.conf

@@ -10,7 +10,14 @@ server {
         try_files $uri $uri.html $uri/ /index.html;
     }
 
-    # Long-cache immutable build assets.
+    # Never cache the HTML shell — so a new deploy (with new chunk hashes) is
+    # always picked up immediately and tabs don't load a stale bundle.
+    location ~* \.html$ {
+        add_header Cache-Control "no-cache, no-store, must-revalidate";
+        try_files $uri /index.html;
+    }
+
+    # Long-cache immutable, content-hashed build assets.
     location /_next/static/ {
         expires 1y;
         add_header Cache-Control "public, immutable";