fix: never cache index.html so new bundle hashes are picked up

Vite content-hashes the JS/CSS bundle filenames, but the only thing
that tells the browser to fetch a new hash is a fresh index.html.
Without explicit no-cache headers nginx falls back to heuristic
caching, so users keep loading the old index.html → old bundle hash
until they hard-reload. Just hit this rolling out the timeline
pagination fix.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/nginx.conf

@@ -35,7 +35,18 @@ server {
         try_files $uri $uri/ /index.html;
     }
 
-    # Cache static assets
+    # Never cache index.html (or any HTML). The asset filenames are
+    # content-hashed by Vite, so a fresh index.html is the only thing
+    # that tells the browser to fetch the new bundle. Without this the
+    # browser happily serves a stale index.html → stale bundle hash →
+    # users see the old build until they hard-reload.
+    location = /index.html {
+        add_header Cache-Control "no-cache, no-store, must-revalidate";
+        add_header Pragma "no-cache";
+        expires 0;
+    }
+
+    # Cache static assets (filenames are content-hashed, so 1y is safe)
     location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
         expires 1y;
         add_header Cache-Control "public, immutable";