feat(web): add AlphabeticalGrid wrapper with letter dividers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/lib/components/AlphabeticalGrid.svelte

@@ -0,0 +1,70 @@
+<script lang="ts" generics="T">
+  import type { Snippet } from 'svelte';
+
+  let {
+    items,
+    getKey,
+    item
+  }: {
+    items: T[];
+    getKey: (it: T) => string;
+    item: Snippet<[T]>;
+  } = $props();
+
+  // Compute the divider letter for each item; if it differs from the
+  // previous item's letter, that index gets a divider above it.
+  const segments = $derived.by(() => {
+    const out: { divider: string | null; item: T }[] = [];
+    let last: string | null = null;
+    for (const it of items) {
+      const k = (getKey(it) || '').charAt(0).toUpperCase();
+      if (k !== last) {
+        out.push({ divider: k, item: it });
+        last = k;
+      } else {
+        out.push({ divider: null, item: it });
+      }
+    }
+    return out;
+  });
+</script>
+
+<div class="alpha-grid">
+  {#each segments as seg, i (i)}
+    {#if seg.divider}
+      <div class="divider">
+        <span class="letter">{seg.divider}</span>
+        <span class="rule"></span>
+      </div>
+    {/if}
+    <div class="cell">
+      {@render item(seg.item)}
+    </div>
+  {/each}
+</div>
+
+<style>
+  .alpha-grid {
+    display: grid;
+    grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
+    gap: 16px;
+  }
+  .divider {
+    grid-column: 1 / -1;
+    display: flex;
+    align-items: center;
+    gap: 12px;
+    padding-top: 8px;
+  }
+  .letter {
+    font-family: var(--fs-font-display);
+    font-size: 24px;
+    font-weight: 500;
+    color: var(--fs-parchment);
+  }
+  .rule {
+    flex: 1;
+    height: 1px;
+    background: var(--fs-pewter);
+  }
+</style>

web/src/lib/components/AlphabeticalGrid.test.ts

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+import { describe, expect, test } from 'vitest';
+import { render, screen } from '@testing-library/svelte';
+import { createRawSnippet } from 'svelte';
+import AlphabeticalGrid from './AlphabeticalGrid.svelte';
+
+type Item = { id: string; key: string; label: string };
+
+const items: Item[] = [
+  { id: '1', key: 'A', label: 'Apple' },
+  { id: '2', key: 'A', label: 'Avocado' },
+  { id: '3', key: 'B', label: 'Banana' },
+  { id: '4', key: 'D', label: 'Date' }   // skips C — divider must jump to D directly
+];
+
+// createRawSnippet<Params> receives getters: each param is () => ParamType
+const itemSnippet = createRawSnippet<[Item]>((getIt) => ({
+  render: () => `<span>${getIt().label}</span>`
+}));
+
+// The generic component's T parameter can't be inferred by testing-library's render,
+// so we cast props to avoid a spurious unknown-assignability error.
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+type AnyProps = any;
+
+describe('AlphabeticalGrid', () => {
+  test('inserts a divider for each new key letter', () => {
+    render(AlphabeticalGrid, {
+      props: {
+        items,
+        getKey: (it: Item) => it.key,
+        item: itemSnippet
+      } as AnyProps
+    });
+    // Three dividers (A, B, D); C is absent because no items use C.
+    expect(screen.getByText('A')).toBeInTheDocument();
+    expect(screen.getByText('B')).toBeInTheDocument();
+    expect(screen.getByText('D')).toBeInTheDocument();
+    expect(screen.queryByText('C')).not.toBeInTheDocument();
+  });
+
+  test('renders items in given order', () => {
+    const { container } = render(AlphabeticalGrid, {
+      props: {
+        items,
+        getKey: (it: Item) => it.key,
+        item: itemSnippet
+      } as AnyProps
+    });
+    expect(container.textContent).toMatch(/A.*Apple.*Avocado.*B.*Banana.*D.*Date/s);
+  });
+});