fix: add grid layout for nested cookbooks in cookbook detail

Added proper grid styling for included/nested cookbooks:
- Added .cookbooks-grid with 5-column grid layout and 1.5rem gap
- Made .cookbook-card.nested explicitly square with aspect-ratio: 1/1
- Added flexbox display to nested cards for proper content layout
- Added responsive mobile styling (1 column on mobile)

This prevents nested cookbooks from displaying as huge squares
that don't respect column sizing.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

packages/web/src/styles/CookbookDetail.css

@@ -571,6 +571,10 @@
   .recipes-grid {
     grid-template-columns: 1fr;
   }
+
+  .included-cookbooks-section .cookbooks-grid {
+    grid-template-columns: 1fr;
+  }
 }
 
 /* Included Cookbooks Section */
@@ -587,11 +591,20 @@
   font-size: 1.5rem;
 }
 
+.included-cookbooks-section .cookbooks-grid {
+  display: grid;
+  grid-template-columns: repeat(5, 1fr);
+  gap: 1.5rem;
+}
+
 .cookbook-card.nested {
   border: 2px solid #e0e0e0;
   background: white;
   cursor: pointer;
   transition: all 0.2s ease;
+  aspect-ratio: 1 / 1;
+  display: flex;
+  flex-direction: column;
 }
 
 .cookbook-card.nested:hover {