fix(titlebar): hide stripped strip in plasma when empty

If the user has search-in-titlebar off AND no titlebar-nav items
enabled, plasma mode would render an empty 42px strip below the KWin
SSD. Gate shouldShowTitleBar() in plasma on whether either is enabled.
+page.svelte's search-location and titlebar-nav subscriptions now
also recompute showTitleBar so the layout reflows immediately when
the user toggles those settings.

cc

src/lib/stores/titleBarStore.ts

@@ -14,6 +14,8 @@
 import { invoke } from '@tauri-apps/api/core';
 import { skipIfRemote } from '$lib/services/commandRouter';
 import { platform } from '$lib/utils/platform';
+import { getSearchBarLocation } from './searchBarLocationStore';
+import { isTitlebarNavEnabled } from './titlebarNavStore';
 
 export type TitlebarMode = 'qbz' | 'system' | 'plasma' | 'hidden';
 
@@ -89,12 +91,20 @@ export function getMode(): TitlebarMode {
 /**
  * Whether the custom TitleBar.svelte component should mount.
  * - macOS always uses native overlay → false.
- * - 'qbz' and 'plasma' → true (full or stripped variant).
+ * - 'qbz' → true (full variant).
+ * - 'plasma' → true ONLY if the stripped strip would carry content
+ *   (search-in-titlebar OR at least one nav item). Otherwise the
+ *   42px strip would render empty below the KWin SSD.
  * - 'system' and 'hidden' → false.
  */
 export function shouldShowTitleBar(): boolean {
   if (platform === 'macos') return false;
-  return mode === 'qbz' || mode === 'plasma';
+  if (mode === 'system' || mode === 'hidden') return false;
+  if (mode === 'qbz') return true;
+  // mode === 'plasma' — only render the strip if it has effective content.
+  // (In plasma, the effective values for search location and titlebar nav
+  //  match the user prefs directly per the derived-state table.)
+  return getSearchBarLocation() === 'titlebar' || isTitlebarNavEnabled();
 }
 
 /**

src/routes/+page.svelte

@@ -4848,6 +4848,10 @@
     initSearchBarLocation();
     const unsubscribeSearchBarLocation = subscribeSearchBarLocation(() => {
       searchBarLocationPref = getEffectiveSearchBarLocation();
+      // In plasma mode the strip's visibility depends on whether search
+      // or any nav item is enabled, so a search-location toggle can flip
+      // the strip on/off.
+      showTitleBar = shouldShowTitleBar();
     });
 
     // Initialize and subscribe to window controls customization
@@ -4868,6 +4872,10 @@
       tbNavLibrary = isLibraryInTitlebar();
       tbNavMyQbz = isMyQbzInTitlebar();
       tbNavPurchases = isPurchasesInTitlebar();
+      // In plasma mode the strip's visibility depends on whether any nav
+      // item or search is enabled, so toggling the last nav item can
+      // flip the strip on/off.
+      showTitleBar = shouldShowTitleBar();
     });
 
     // Detect floating window state (not maximized) for rounded corners + shadow