fix(site-builder): never save before a successful load; guard empty overwrites

Refs #28

craft/src/styles/editor.css

@@ -1929,3 +1929,48 @@ body {
   background: var(--color-bg-hover);
   color: var(--color-text);
 }
+
+/* Blocking overlay while the initial project load runs / has failed. Covers
+   everything below the topbar so nothing is editable behind it. */
+.load-gate {
+  position: fixed;
+  top: 48px;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  z-index: var(--z-modal);
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: 12px;
+  background: rgba(15, 23, 42, 0.92);
+  color: #e2e8f0;
+  font-size: 14px;
+}
+.load-gate p { margin: 0; }
+
+.empty-save-banner {
+  position: absolute;
+  top: 100%;
+  left: 0;
+  right: 0;
+  z-index: 41;
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 10px 12px;
+  background: #450a0a;
+  border-bottom: 1px solid #b91c1c;
+  color: #fecaca;
+  font-size: 12px;
+}
+.empty-save-banner-text { flex: 1; }
+.empty-save-banner button {
+  background: none;
+  border: 1px solid #fecaca;
+  border-radius: 4px;
+  color: #fecaca;
+  cursor: pointer;
+  padding: 2px 10px;
+}