feat(PerspectivePlan): add a wrapper to work with perspective manager styles

src/shared/ui/PerspectivePlan/PerspectivePlan.svelte

@@ -0,0 +1,83 @@
+<!--
+    Component: PerspectivePlan
+    Wrapper that applies perspective transformations based on back/front state.
+    Style computation moved from manager to component for simpler architecture.
+-->
+<script lang="ts">
+import type { PerspectiveManager } from '$shared/lib';
+import { cn } from '$shared/shadcn/utils/shadcn-utils';
+import { type Snippet } from 'svelte';
+
+interface Props {
+    /**
+     * Perspective manager
+     */
+    manager: PerspectiveManager;
+    /**
+     * Additional classes
+     */
+    class?: string;
+    /**
+     * Children
+     */
+    children: Snippet<[{ className?: string }]>;
+    /**
+     * Constrain plan to a horizontal region
+     * 'left' | 'right' | 'full' (default)
+     */
+    region?: 'left' | 'right' | 'full';
+    /**
+     * Width percentage when using left/right region (default 50)
+     */
+    regionWidth?: number;
+}
+
+let { manager, children, class: className = '', region = 'full', regionWidth = 50 }: Props = $props();
+
+const config = $derived(manager.getConfig());
+
+// Computed style based on spring position (0 = front, 1 = back)
+const style = $derived.by(() => {
+    const distance = manager.spring.current;
+    const baseX = config.horizontalOffset ?? 0;
+
+    // Back state: blurred, scaled down, pushed back
+    // Front state: fully visible, in focus
+    const scale = 1 - distance * (config.scaleStep ?? 0.5);
+    const blur = distance * (config.blurStep ?? 4);
+    const opacity = Math.max(0, 1 - distance * (config.opacityStep ?? 0.5));
+    const zIndex = 10;
+    const pointerEvents = distance < 0.4 ? 'auto' : ('none' as const);
+
+    return {
+        transform: `translate3d(${baseX}px, 0px, ${-distance * (config.depthStep ?? 100)}px) scale(${scale})`,
+        filter: `blur(${blur}px)`,
+        opacity,
+        pointerEvents,
+        zIndex,
+    };
+});
+
+// Calculate horizontal constraints based on region
+const regionStyleStr = $derived(() => {
+    if (region === 'full') return '';
+    const side = region === 'left' ? 'left' : 'right';
+    return `position: absolute; ${side}: 0; width: ${regionWidth}%; top: 0; bottom: 0;`;
+});
+
+// Visibility: front = visible, back = hidden
+const isVisible = $derived(manager.isFront);
+</script>
+
+<div
+    class={cn('will-change-transform', className)}
+    style:transform-style="preserve-3d"
+    style:transform={style?.transform}
+    style:filter={style?.filter}
+    style:opacity={style?.opacity}
+    style:pointer-events={style?.pointerEvents}
+    style:z-index={style?.zIndex}
+    style:custom={regionStyleStr()}
+>
+    {@render children({ className: isVisible ? 'visible' : 'hidden' })}
+</div>