Optimize: pre-lowercase filter values to avoid redundant conversions

Co-authored-by: garrytrinder <11563347+garrytrinder@users.noreply.github.com>

Author: Copilot

src/components/SampleGallery.astro

@@ -153,13 +153,13 @@ function getMetadataMap(sample: CollectionEntry<'samples'>): Record<string, stri
   function applyFilters() {
     const query = searchInput.value.toLowerCase().trim();
 
-    // Collect active metadata filters
+    // Collect active metadata filters (pre-lowercase values for comparison)
     const activeFilters: Record<string, string> = {};
     filterSelects.forEach((select) => {
       const key = select.dataset.filterKey!;
       const value = select.value;
       if (value) {
-        activeFilters[key] = value;
+        activeFilters[key] = value.toLowerCase();
       }
     });
 
@@ -177,7 +177,7 @@ function getMetadataMap(sample: CollectionEntry<'samples'>): Record<string, stri
       // Metadata filter match (all active filters must match)
       let metadataMatch = true;
       for (const [key, value] of Object.entries(activeFilters)) {
-        if ((metadata[key] || '').toLowerCase() !== value.toLowerCase()) {
+        if ((metadata[key] || '').toLowerCase() !== value) {
           metadataMatch = false;
           break;
         }