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).

static/css/04-interactive/_buttons.css

@@ -176,6 +176,72 @@
    The 900px media query there uses clamp() for smooth scaling of all buttons and icons */
 
 
+/* =============================================================================
+   CMD+K SEARCH BAR BUTTON (Integrated in Action Bar)
+   ============================================================================= */
+
+/* Search bar button - styled to look like a search input within the dark action bar */
+.search-bar-btn {
+    display: flex !important;
+    align-items: center;
+    gap: 0.5rem;
+    padding: 0.35rem 0.6rem !important;
+    background: rgba(255, 255, 255, 0.1) !important;
+    border: 1px solid rgba(255, 255, 255, 0.2) !important;
+    border-radius: 6px !important;
+    min-width: 140px;
+    transition: all 0.2s ease;
+}
+
+.search-bar-btn:hover {
+    background: rgba(255, 255, 255, 0.15) !important;
+    border-color: rgba(255, 255, 255, 0.3) !important;
+}
+
+.search-bar-icon {
+    color: rgba(255, 255, 255, 0.6);
+    flex-shrink: 0;
+}
+
+.search-bar-text {
+    color: rgba(255, 255, 255, 0.6);
+    font-size: 0.8rem;
+    flex-grow: 1;
+    text-align: left;
+}
+
+.search-bar-keys {
+    display: flex;
+    align-items: center;
+    gap: 0.2rem;
+    flex-shrink: 0;
+}
+
+.search-bar-keys kbd {
+    font-family: -apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif;
+    font-size: 0.65rem;
+    font-weight: 500;
+    color: rgba(255, 255, 255, 0.7);
+    background: rgba(255, 255, 255, 0.15);
+    border: 1px solid rgba(255, 255, 255, 0.25);
+    border-radius: 3px;
+    padding: 0.1rem 0.3rem;
+    min-width: 1.2rem;
+    text-align: center;
+}
+
+/* Hide kbd keys on smaller screens to save space */
+@media (max-width: 900px) {
+    .search-bar-keys {
+        display: none;
+    }
+
+    .search-bar-btn {
+        min-width: auto;
+    }
+}
+
+
 /* =============================================================================
    NINJA-KEYS COMMAND BAR STYLING
    ============================================================================= */