Fix nginx: rewrite font paths in CSS to prevent double fonts/ directory (STI-91)

GrampsWeb's fonts.css references fonts as url('fonts/MaterialIcons.woff2').
Since fonts.css is served from /ahnenforschung/fonts/fonts.css, the browser
resolves this to /ahnenforschung/fonts/fonts/MaterialIcons.woff2 (double
fonts/ directory). Strip the fonts/ prefix via sub_filter so the URL
resolves correctly to /ahnenforschung/fonts/MaterialIcons.woff2.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

deploy-production/nginx.conf

@@ -126,7 +126,11 @@ server {
         # JS: service worker route handling
         sub_filter 'createHandlerBoundToURL("/index.html")' 'createHandlerBoundToURL("/ahnenforschung/index.html")';
 
-        # CSS: font paths — ../fonts/ resolves correctly from subpath, no rewrite needed
+        # CSS: fix font paths in fonts.css — the CSS lives at /ahnenforschung/fonts/fonts.css
+        # and references url('fonts/MaterialIcons.woff2') which resolves to
+        # /ahnenforschung/fonts/fonts/MaterialIcons.woff2 (double fonts/).
+        # Strip the fonts/ prefix so url('MaterialIcons.woff2') resolves correctly.
+        sub_filter "url('fonts/" "url('";
 
         # WebSocket support
         proxy_http_version 1.1;