feat(LayoutManager): create layout manager with persistent store support to manage SampleList items layout

src/widgets/SampleList/model/stores/layoutStore/layoutStore.svelte.ts

@@ -0,0 +1,113 @@
+import { createPersistentStore } from '$shared/lib';
+import { responsiveManager } from '$shared/lib';
+
+export type LayoutMode = 'list' | 'grid';
+
+interface LayoutConfig {
+    mode: LayoutMode;
+}
+
+const STORAGE_KEY = 'glyphdiff:sample-list-layout';
+const SM_GAP_PX = 16;
+const MD_GAP_PX = 24;
+
+const DEFAULT_CONFIG: LayoutConfig = {
+    mode: 'list',
+};
+
+/**
+ * LayoutManager manages the layout configuration for SampleList widget.
+ * Handles mode switching between list/grid and responsive column calculation.
+ */
+class LayoutManager {
+    // Private reactive state
+    #mode = $state<LayoutMode>(DEFAULT_CONFIG.mode);
+    #store = createPersistentStore<LayoutConfig>(STORAGE_KEY, DEFAULT_CONFIG);
+
+    constructor() {
+        // Load saved layout preference
+        const saved = this.#store.value;
+        if (saved && saved.mode) {
+            this.#mode = saved.mode;
+        }
+    }
+
+    get mode(): LayoutMode {
+        return this.#mode;
+    }
+
+    get gap(): number {
+        return responsiveManager.isMobile || responsiveManager.isTabletPortrait ? SM_GAP_PX : MD_GAP_PX;
+    }
+
+    get isListMode(): boolean {
+        return this.#mode === 'list';
+    }
+
+    get isGridMode(): boolean {
+        return this.#mode === 'grid';
+    }
+
+    /**
+     * Get current number of columns based on mode and screen size.
+     * List mode always uses 1 column.
+     * Grid mode uses responsive column counts:
+     * - Mobile: 1 column
+     * - Tablet Portrait: 1 column
+     * - Tablet: 2 columns
+     * - Desktop: 3 columns
+     * - Desktop Large: 4 columns
+     */
+    get columns(): number {
+        if (this.#mode === 'list') {
+            return 1;
+        }
+
+        // Grid mode: responsive columns
+        switch (true) {
+            case responsiveManager.isMobile:
+                return 1;
+            case responsiveManager.isTabletPortrait:
+                return 1;
+            case responsiveManager.isTablet:
+                return 2;
+            case responsiveManager.isDesktop:
+                return 3;
+            case responsiveManager.isDesktopLarge:
+                return 4;
+            default:
+                return 1;
+        }
+    }
+
+    /**
+     * Set the layout mode.
+     * @param mode - The new layout mode ('list' or 'grid')
+     */
+    setMode(mode: LayoutMode): void {
+        if (this.#mode === mode) {
+            return;
+        }
+
+        this.#mode = mode;
+        this.#store.value = { mode };
+    }
+
+    /**
+     * Toggle between list and grid modes.
+     */
+    toggleMode(): void {
+        this.setMode(this.#mode === 'list' ? 'grid' : 'list');
+    }
+
+    /**
+     * Reset to default layout mode.
+     */
+    reset(): void {
+        this.#mode = DEFAULT_CONFIG.mode;
+        this.#store.clear();
+    }
+}
+
+// Export a singleton — one instance for the whole app
+export const layoutManager = new LayoutManager();