topbar: surface publish warnings instead of discarding them

handlePublish's JSON response has always included a `warnings` array
(e.g. the contact-form relay's "submissions will not be delivered"
notice), but nothing in the editor ever read it. Adds a PublishWarnings
banner, held in its own state independent of the 3s publishStatus
flash so the customer has time to read it, rendered in both the
desktop and mobile TopBar branches.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/styles/editor.css

@@ -106,6 +106,11 @@ body {
   border-bottom: 1px solid var(--color-border);
   z-index: 100;
   gap: 12px;
+  /* Positioned ancestor for .publish-warnings (position: absolute; top:
+     100%), which is rendered as this <nav>'s first child in both the
+     desktop and mobile branches -- without this, it would anchor to the
+     viewport instead of sitting directly under the topbar. */
+  position: relative;
 }
 
 .topbar-left,
@@ -1884,3 +1889,33 @@ body {
     height: 44px !important;
   }
 }
+
+/* --------------------------------------------------------------------------
+   Publish warnings banner -- non-blocking; the site DID publish. Anchored
+   to .topbar's `position: relative` (see above) so it drops down directly
+   beneath the bar in both the desktop and mobile branches.
+   -------------------------------------------------------------------------- */
+.publish-warnings {
+  position: absolute;
+  top: 100%;
+  left: 0;
+  right: 0;
+  z-index: 40;
+  display: flex;
+  align-items: flex-start;
+  gap: 8px;
+  padding: 10px 12px;
+  background: #422006;
+  border-bottom: 1px solid #a16207;
+  color: #fde68a;
+  font-size: 12px;
+}
+.publish-warnings ul { margin: 0; padding-left: 16px; flex: 1; }
+.publish-warnings li { margin: 2px 0; }
+.publish-warnings button {
+  background: none;
+  border: none;
+  color: #fde68a;
+  cursor: pointer;
+  padding: 0 4px;
+}