feat: add missing storybook files and type template arguments properly

src/entities/Breadcrumb/ui/BreadcrumbHeader/BreadcrumbHeader.stories.svelte

@@ -0,0 +1,65 @@
+<script module>
+import { defineMeta } from '@storybook/addon-svelte-csf';
+import BreadcrumbHeader from './BreadcrumbHeader.svelte';
+
+const { Story } = defineMeta({
+    title: 'Entities/BreadcrumbHeader',
+    component: BreadcrumbHeader,
+    tags: ['autodocs'],
+    parameters: {
+        docs: {
+            description: {
+                component:
+                    'Fixed header that slides in when the user scrolls past tracked page sections. Reads `scrollBreadcrumbsStore.scrolledPastItems` — renders nothing when the list is empty. Requires the `responsive` context provided by `Providers`.',
+            },
+            story: { inline: false },
+        },
+        layout: 'fullscreen',
+    },
+    argTypes: {},
+});
+</script>
+
+<script>
+import Providers from '$shared/lib/storybook/Providers.svelte';
+import BreadcrumbHeaderSeeded from './BreadcrumbHeaderSeeded.svelte';
+</script>
+
+<Story
+    name="With Breadcrumbs"
+    parameters={{
+        docs: {
+            description: {
+                story:
+                    'Three sections are registered with the breadcrumb store. The story scrolls the iframe so the IntersectionObserver marks them as scrolled-past, revealing the fixed header.',
+            },
+        },
+    }}
+>
+    {#snippet template()}
+        <Providers>
+            <BreadcrumbHeaderSeeded />
+        </Providers>
+    {/snippet}
+</Story>
+
+<Story
+    name="Empty"
+    parameters={{
+        docs: {
+            description: {
+                story:
+                    'No sections registered — BreadcrumbHeader renders nothing. This is the initial state before the user scrolls past any tracked section.',
+            },
+        },
+    }}
+>
+    {#snippet template()}
+        <Providers>
+            <div style="padding: 2rem; color: #888; font-size: 0.875rem;">
+                BreadcrumbHeader renders nothing when scrolledPastItems is empty.
+            </div>
+            <BreadcrumbHeader />
+        </Providers>
+    {/snippet}
+</Story>

src/entities/Breadcrumb/ui/BreadcrumbHeader/BreadcrumbHeaderSeeded.svelte

@@ -0,0 +1,49 @@
+<script>
+import { onMount } from 'svelte';
+import { scrollBreadcrumbsStore } from '../../model';
+import BreadcrumbHeader from './BreadcrumbHeader.svelte';
+
+const sections = [
+    { index: 100, title: 'Introduction' },
+    { index: 101, title: 'Typography' },
+    { index: 102, title: 'Spacing' },
+];
+
+/** @type {HTMLDivElement} */
+let container;
+
+onMount(() => {
+    for (const section of sections) {
+        const el = /** @type {HTMLElement} */ (container.querySelector(`[data-story-index="${section.index}"]`));
+        scrollBreadcrumbsStore.add({ index: section.index, title: section.title, element: el }, 96);
+    }
+
+    /*
+     * Scroll past the sections so IntersectionObserver marks them as
+     * scrolled-past, making scrolledPastItems non-empty and the header visible.
+     */
+    setTimeout(() => {
+        window.scrollTo({ top: 2000, behavior: 'instant' });
+    }, 100);
+
+    return () => {
+        for (const { index } of sections) {
+            scrollBreadcrumbsStore.remove(index);
+        }
+        window.scrollTo({ top: 0, behavior: 'instant' });
+    };
+});
+</script>
+
+<div bind:this={container} style="height: 2400px; padding-top: 900px;">
+    {#each sections as section}
+        <div
+            data-story-index={section.index}
+            style="height: 400px; padding: 2rem; background: #f5f5f5; margin-bottom: 1rem;"
+        >
+            {section.title} — scroll up to see the breadcrumb header
+        </div>
+    {/each}
+</div>
+
+<BreadcrumbHeader />