feat: style reset button and override OG image on forms.nhcarrigan.com

- Style .test-form-reset with theme accent colour (#A8577E) for readability
- Replace Grist default OG image URL directly so all three meta tags use the nhcarrigan CDN image

nginx/nginx/sites-available/forms.conf

@@ -96,6 +96,9 @@ server {
         # Disable Gzip from upstream so nginx can inject CSS
         proxy_set_header Accept-Encoding "";
 
+        # Override Grist OG image (replace the URL directly so our image wins in all three tags)
+        sub_filter 'https://grist-static.com/icons/opengraph-preview-image.png' 'https://cdn.nhcarrigan.com/og-image.png';
+
         # Inject CSS and remove Grist branding
         sub_filter '</body>' '<style>
             /* 1. Remove the "Powered by Grist" footer */
@@ -114,6 +117,13 @@ server {
                 display: none !important;
             }
 
+            /* 4. Style the reset button with the theme accent colour */
+            .test-form-reset {
+                background-color: #A8577E !important;
+                border-color: #A8577E !important;
+                color: #F5F5F5 !important;
+            }
+
 	    main {
 		margin-bottom: auto !important;
 	   }
@@ -125,7 +135,7 @@ server {
         </style><script src="https://cdn.nhcarrigan.com/headers/index.js"></script><script>document.querySelector("footer")?.remove();</script>
 </body>';
 
-        sub_filter_once on;
+        sub_filter_once off;
     }
 
     # Upgrade websocket requests and route the api backend