feat: redesign CMD+K button as macOS Spotlight-style search bar

Replace simple search button with search bar design in action bar:
- Semi-transparent styling integrated with dark action bar
- Keyboard shortcut indicators (⌘ K) shown as individual kbd elements
- Search icon and "Search" text for better discoverability
- Responsive: kbd keys hidden on mobile (<900px)
- Remove unused cmd-k-button.html partial template

Update test to verify new search bar structure (styling, kbd elements, icon).

templates/partials/navigation/action-buttons.html

@@ -24,11 +24,15 @@
         {{.UI.Widgets.ActionButtons.PrintFriendly}}
     </button>
     <button
-        class="action-btn search-btn has-tooltip cmd-k-trigger"
-        aria-label="{{.UI.Widgets.ActionButtons.SearchAriaLabel}}"
-        data-tooltip="{{.UI.Widgets.ActionButtons.Search}}">
-        <iconify-icon icon="mdi:magnify" width="24" height="24"></iconify-icon>
-        {{.UI.Widgets.ActionButtons.Search}}
+        id="cmd-k-button"
+        class="action-btn search-bar-btn cmd-k-trigger"
+        aria-label="{{.UI.Widgets.ActionButtons.SearchAriaLabel}}">
+        <iconify-icon icon="mdi:magnify" width="18" height="18" class="search-bar-icon"></iconify-icon>
+        <span class="search-bar-text">{{.UI.Widgets.ActionButtons.Search}}</span>
+        <span class="search-bar-keys">
+            <kbd>⌘</kbd>
+            <kbd>K</kbd>
+        </span>
     </button>
 </div>
 {{end}}

templates/partials/widgets/cmd-k-button.html

@@ -1,11 +0,0 @@
-{{define "cmd-k-button"}}
-<!-- CMD+K Command Bar Button (Fixed Left - Last) -->
-<!-- Uses lazy loading - ninja-keys loads on first click -->
-<button
-    id="cmd-k-button"
-    class="fixed-btn cmd-k-btn no-print has-tooltip cmd-k-trigger"
-    aria-label="{{.UI.CmdK.Button.AriaLabel}}"
-    data-tooltip="{{.UI.CmdK.Button.Tooltip}}">
-    <iconify-icon icon="mdi:text-box-search-outline"></iconify-icon>
-</button>
-{{end}}