edit page: thumbnail + edit-details cards span both columns

Per fox: "🎨 Upload or Replace Thumbnail Files ... should be in a row
that spans two columns" — and the same for "Edit Title, Description,
or Visibility".

Both cards now get class edit-card-full, which sets grid-column: 1 / -1
so they span the entire row in the 2-column edit grid. The thumbnail
grid has up to 4 thumbnails that need room; the edit-details card
has a wide form with pricing-mode radios and description textarea.

New CSS:
  div.edit-page > section.edit-card-full { grid-column: 1 / -1; }

Styleguide updated with a live half/half/full example demonstrating
the pattern.

make_post_sell/GIT_HASH

@@ -1 +1 @@
-705271e
+86790b7

make_post_sell/static/css/common.css

@@ -1562,6 +1562,23 @@ div.edit-page button.mps-submit-primary:disabled,
     font-size: 0.9em;
 }
 
+/* Full-width edit card — spans both columns of the 2-col edit grid.
+   Used for sections that have grid layouts of their own (thumbnails,
+   bundle products) where 1 column doesn't give enough room. */
+div.edit-page > section.edit-card-full {
+    grid-column: 1 / -1;
+}
+
+/* On the thumbnails card the descriptor section (Your cover ... will
+   show up on search pages) sits to the right of the h3 header inside
+   the section.upload-thumbnails inner grid. Right-align its text so
+   it reads as a caption beside the header. */
+section.upload-thumbnails > section:first-of-type {
+    text-align: right;
+    justify-self: end;
+    align-self: center;
+}
+
 hr {
   color: var(--border-light, #EEEEEE);
 }

make_post_sell/templates/product_edit.j2

@@ -201,7 +201,7 @@ permanent link: <a href="{{ product.absolute_url(request) }}">{{ product.absolut
 
 </section>
 
-<section class="upload-thumbnails well2">
+<section class="upload-thumbnails well2 edit-card-full">
 <h3>
   <span class="edit-card-icon">&#127912;</span>
   Upload or Replace Thumbnail Files
@@ -263,7 +263,7 @@ Your cover (<code>thumbnail1</code>) will show up on search pages.
 {% endfor %}
 </section>
 
-<section class="product-title-and-description well2">
+<section class="product-title-and-description well2 edit-card-full">
   <form method="post" action="{{ product.absolute_edit_url(request) }}" onsubmit="submit.disabled = true; return true;">
   <h3>
     <span class="edit-card-icon">&#9998;</span>

make_post_sell/templates/styleguide.j2

@@ -1132,6 +1132,23 @@ CSS:      .login-card, .login-form-*</div>
   <p>The Save Settings button on the edit page is rendered as a filled, prominent CTA — navy background, bold weight, elevation shadow that lifts on hover. Class <code>mps-button-primary</code>.</p>
   <button class="mps-button-primary" style="margin-bottom: var(--space-4);">Save Settings</button>
 
+  <h3>Full-width card (spans both columns)</h3>
+  <p>For sections that need extra horizontal room (thumbnail grid, bundle list), add <code>edit-card-full</code> to the well's class list. It spans the entire row in the 2-column edit grid.</p>
+  <div class="edit-page" style="grid-template-columns: 1fr 1fr; max-width: 100%; padding: 0; margin: var(--space-3) 0 var(--space-5);">
+    <section class="well2">
+      <h3><span class="edit-card-icon">&#128193;</span> Half-width card</h3>
+      <p>This is a single-column card.</p>
+    </section>
+    <section class="well2">
+      <h3><span class="edit-card-icon">&#9998;</span> Half-width card</h3>
+      <p>This is a single-column card.</p>
+    </section>
+    <section class="well2 edit-card-full">
+      <h3><span class="edit-card-icon">&#127912;</span> Full-width card</h3>
+      <p>This card spans both columns — useful for thumbnail grids and other content that needs room to breathe.</p>
+    </section>
+  </div>
+
   <h3>File metadata line</h3>
   <p>Stack file type and size on a single line with a · separator. Use class <code>file-meta</code> on the wrapping <code>&lt;p&gt;</code> and <code>file-meta-item</code> on each child span.</p>
   <div class="well" style="margin-bottom: var(--space-4);">