style(fe): standardize filter section height across all pages

PageLayout:
- Filter section: min-height 52px (standard height)
- Display: flex with center alignment
- Consistent gap between elements

ModelsList:
- Filter container: align-items center
- Remove bottom margin (handled by PageLayout)

Ensures all pages have consistent filter bar heights
and alignment without per-page CSS adjustments.

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

frontend/src/features/models/pages/ModelsList.vue

@@ -185,8 +185,8 @@ function handleSearch() {
 <style scoped>
 .filters {
   display: flex;
+  align-items: center;
   gap: var(--kbx-spacing-md, 1rem);
-  margin-bottom: var(--kbx-spacing-md, 1rem);
 }
 
 .search-input,