Add dedicated subscribe page and seed all JSON defaults on startup

src/App.css

@@ -774,6 +774,20 @@
   padding: 0;
 }
 
+.subscribe-card {
+  max-width: 560px;
+}
+
+.subscribe-form {
+  margin-top: 1rem;
+  text-align: left;
+}
+
+.subscribe-form .btn-secondary {
+  width: 100%;
+  justify-content: center;
+}
+
 .thanks-countdown {
   color: #d4b87a !important;
   letter-spacing: 0.06em;