Replace store dropdown with checkbox toggle chips

Each store appears as a clickable chip with a checkmark. Click to
exclude a store from results (greys out with strikethrough). Click
again to re-include. Multiple stores can be toggled independently.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/src/routes/results/+page.svelte

@@ -11,7 +11,7 @@
   let sortBy = $state('price');
   let sortAsc = $state(true);
   let filterText = $state('');
-  let filterStore = $state('');
+  let excludedStores = $state(new Set());
 
   onMount(async () => {
     const params = $page.url.searchParams;
@@ -72,8 +72,8 @@
     }
 
     // Store filter
-    if (filterStore) {
-      items = items.filter(r => r.storeName === filterStore);
+    if (excludedStores.size > 0) {
+      items = items.filter(r => !excludedStores.has(r.storeName));
     }
 
     // Sort
@@ -102,6 +102,13 @@
     catch { return `${currency} ${price.toFixed(2)}`; }
   }
 
+  function toggleStore(name) {
+    const next = new Set(excludedStores);
+    if (next.has(name)) next.delete(name);
+    else next.add(name);
+    excludedStores = next;
+  }
+
   function sortIcon(column) {
     if (sortBy !== column) return '';
     return sortAsc ? '\u2191' : '\u2193';
@@ -154,15 +161,32 @@
                  text-text-primary placeholder-text-tertiary focus:border-accent/50 focus:outline-none transition-colors" />
       </div>
 
-      <select bind:value={filterStore} class="input-field w-auto text-xs py-1 px-2">
-        <option value="">All stores</option>
+      <div class="flex items-center gap-1.5">
         {#each storeNames() as name}
-          <option value={name}>{name}</option>
+          <button
+            onclick={() => toggleStore(name)}
+            class="flex items-center gap-1.5 text-2xs px-2 py-1 rounded border transition-colors duration-100
+              {excludedStores.has(name)
+                ? 'bg-surface border-surface-border text-text-tertiary line-through opacity-50 hover:opacity-75'
+                : 'bg-accent-muted border-accent/30 text-accent-text hover:bg-accent/20'}"
+          >
+            <span class="w-3 h-3 rounded-sm border flex items-center justify-center flex-shrink-0
+              {excludedStores.has(name)
+                ? 'border-text-tertiary/30'
+                : 'border-accent/50 bg-accent/20'}">
+              {#if !excludedStores.has(name)}
+                <svg class="w-2 h-2 text-accent-text" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="3">
+                  <path stroke-linecap="round" stroke-linejoin="round" d="M4.5 12.75l6 6 9-13.5" />
+                </svg>
+              {/if}
+            </span>
+            {name}
+          </button>
         {/each}
-      </select>
+      </div>
 
-      <span class="text-2xs text-text-tertiary">
-        {filteredAndSorted().length} of {results.length} shown
+      <span class="text-2xs text-text-tertiary whitespace-nowrap">
+        {filteredAndSorted().length} of {results.length}
       </span>
     </div>
   {/if}