refactor(frontend): Separate keyboard filter mode from regular dropdown

The keyboard filter modal and regular dropdown now use independent state:
- Keyboard modal controlled by isFilterModeActive store
- Regular dropdown controlled by local isOpen state
- Escape handler handles each case separately

This fixes the issue where the regular dropdown would appear after
closing the keyboard filter modal, and removes the code smell of
sharing state between two different UI modes.

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

Author: enko

apps/frontend/src/lib/components/search/FacetDropdown.svelte

@@ -108,11 +108,9 @@ let currentCategoryValues = $derived(
   $filterModeCategory ? getCategoryValues($filterModeCategory) : [],
 );
 
-// Auto-open dropdown when filter mode activates and scroll to selected section
+// Auto-scroll to selected section when filter mode activates
 $effect(() => {
   if ($isFilterModeActive && $filterModeCategory) {
-    isOpen = true;
-
     // Scroll to the selected category section after the modal renders
     tick().then(() => {
       const category = $filterModeCategory;
@@ -139,21 +137,18 @@ $effect(() => {
   }
 });
 
-// Close modal when filter mode is deactivated
-$effect(() => {
-  if (!$isFilterModeActive && isOpen) {
-    // Don't auto-close on mode deactivation - let user close manually or via Escape
-  }
-});
-
-// Close modal and clear filter mode
-function closeModal() {
-  isOpen = false;
+// Close keyboard filter mode
+function closeKeyboardFilterMode() {
   isFilterModeActive.set(false);
   filterModeCategory.set(null);
   filterModePrefix.set(null);
 }
 
+// Close regular dropdown
+function closeDropdown() {
+  isOpen = false;
+}
+
 // Method to toggle filter by index (called from keyboard shortcuts)
 export function toggleFilterByIndex(index: number) {
   if (index < 0 || index >= currentCategoryValues.length) return;
@@ -211,13 +206,19 @@ $effect(() => {
 });
 </script>
 
-<!-- Handle Escape key to close modal -->
+<!-- Handle Escape key to close keyboard filter mode or dropdown -->
 <svelte:window
   onkeydown={(e) => {
-    if (e.key === 'Escape' && isOpen) {
-      e.preventDefault();
-      e.stopPropagation();
-      closeModal();
+    if (e.key === 'Escape') {
+      if ($isFilterModeActive) {
+        e.preventDefault();
+        e.stopPropagation();
+        closeKeyboardFilterMode();
+      } else if (isOpen) {
+        e.preventDefault();
+        e.stopPropagation();
+        closeDropdown();
+      }
     }
   }}
 />
@@ -269,14 +270,14 @@ $effect(() => {
     {/if}
   </button>
 
-  <!-- Modal overlay for keyboard mode -->
-  {#if isOpen && hasFacets && $isFilterModeActive}
+  <!-- Modal overlay for keyboard mode (independent of isOpen) -->
+  {#if hasFacets && $isFilterModeActive && $filterModeCategory}
     <!-- svelte-ignore a11y_no_static_element_interactions -->
     <!-- svelte-ignore a11y_click_events_have_key_events -->
     <!-- svelte-ignore a11y_interactive_supports_focus -->
     <div
       class="fixed inset-0 bg-black bg-opacity-50 z-50 flex items-center justify-center p-4"
-      onclick={closeModal}
+      onclick={closeKeyboardFilterMode}
       role="dialog"
       aria-modal="true"
       aria-label="Filter selection"
@@ -290,7 +291,7 @@ $effect(() => {
         <div class="sticky top-0 bg-white border-b border-gray-200 px-4 py-3 flex items-center justify-between">
           <h2 class="text-lg font-heading text-forest">Filters</h2>
           <button
-            onclick={closeModal}
+            onclick={closeKeyboardFilterMode}
             class="p-2 text-gray-500 hover:text-gray-700 rounded-lg hover:bg-gray-100"
             aria-label="Close"
           >
@@ -448,8 +449,10 @@ $effect(() => {
         </div>
       </div>
     </div>
+  {/if}
+
   <!-- Regular dropdown for non-keyboard mode -->
-  {:else if isOpen && hasFacets}
+  {#if isOpen && hasFacets && !$isFilterModeActive}
     <div
       class="absolute left-0 top-full mt-2 w-72 bg-white rounded-lg shadow-xl border border-gray-200 z-50 p-4 max-h-80 overflow-y-auto"
     >