feat(shared): add Avatar primitive — sizes 26/28/40/48, stacked, overflow chip (§5)

Refs #855
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/shared/primitives/Avatar.svelte

@@ -0,0 +1,94 @@
+<script lang="ts">
+import { avatarFor } from '$lib/shared/avatar';
+
+type AvatarSize = 26 | 28 | 40 | 48;
+
+interface Props {
+	/** Person name — plain string, never a domain entity */
+	name?: string;
+	/** Visual size in px */
+	size?: AvatarSize;
+	/** Stacked variant: negative margin + ring-surface ring */
+	stacked?: boolean;
+	/**
+	 * a11y mode:
+	 * - true (default when name is adjacent in layout) → aria-hidden
+	 * - false → role="img" + aria-label=name
+	 */
+	decorative?: boolean;
+	/**
+	 * Overflow chip mode — renders "+N" instead of initials.
+	 * When set, name/initials are ignored.
+	 */
+	overflow?: number;
+	/**
+	 * Placeholder mode — dashed border empty circle (for ContributorStack empty state).
+	 */
+	placeholder?: boolean;
+}
+
+let {
+	name = '',
+	size = 40,
+	stacked = false,
+	decorative = true,
+	overflow,
+	placeholder = false
+}: Props = $props();
+
+const avatar = $derived(avatarFor(name));
+
+const sizeClass: Record<AvatarSize, string> = {
+	26: 'h-[26px] w-[26px] text-[10px]',
+	28: 'h-[28px] w-[28px] text-[11px]',
+	40: 'h-[40px] w-[40px] text-[14px]',
+	48: 'h-[48px] w-[48px] text-[16px]'
+};
+
+const classes = $derived(
+	[
+		'inline-flex shrink-0 items-center justify-center rounded-full font-sans font-bold text-white transition-colors',
+		sizeClass[size] ?? sizeClass[40],
+		stacked ? '-ml-1.5 ring-2 ring-surface dark:ring-surface' : '',
+		placeholder ? 'border border-dashed border-line bg-transparent text-transparent' : ''
+	]
+		.filter(Boolean)
+		.join(' ')
+);
+</script>
+
+{#if overflow !== undefined}
+	<!-- Overflow "+N" chip -->
+	<span
+		data-testid="avatar"
+		class="{classes} bg-muted text-ink-3"
+		role="img"
+		aria-label="Weitere Personen"
+	>
+		+{overflow}
+	</span>
+{:else if placeholder}
+	<!-- Empty placeholder (dashed border, no background) -->
+	<span data-testid="avatar" class={classes} role="img" aria-label="Noch niemand angefangen"></span>
+{:else if decorative}
+	<!-- Decorative: name is adjacent in layout — aria-hidden="true" -->
+	<span
+		data-testid="avatar"
+		class={classes}
+		style="background-color: {avatar.bg}"
+		aria-hidden="true"
+	>
+		{avatar.initials}
+	</span>
+{:else}
+	<!-- Standalone: expose name to screen readers via role="img" + aria-label -->
+	<span
+		data-testid="avatar"
+		class={classes}
+		style="background-color: {avatar.bg}"
+		role="img"
+		aria-label={name}
+	>
+		{avatar.initials}
+	</span>
+{/if}

frontend/src/lib/shared/primitives/Avatar.svelte.spec.ts

@@ -0,0 +1,105 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+
+import Avatar from './Avatar.svelte';
+
+afterEach(() => cleanup());
+
+function getAvatar(): HTMLElement | null {
+	return document.querySelector('[data-testid="avatar"]');
+}
+
+describe('Avatar', () => {
+	it('renders initials from name', async () => {
+		render(Avatar, { name: 'Anna Raddatz' });
+		await expect.element(page.getByText('AR')).toBeInTheDocument();
+	});
+
+	it('applies size-26 class for size=26', async () => {
+		render(Avatar, { name: 'Anna Raddatz', size: 26 });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		expect(el!.className).toMatch(/h-\[26px\]/);
+		expect(el!.className).toMatch(/w-\[26px\]/);
+	});
+
+	it('applies size-28 class for size=28', async () => {
+		render(Avatar, { name: 'Karl Müller', size: 28 });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		expect(el!.className).toMatch(/h-\[28px\]/);
+		expect(el!.className).toMatch(/w-\[28px\]/);
+	});
+
+	it('applies size-40 class for size=40', async () => {
+		render(Avatar, { name: 'Karl Müller', size: 40 });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		expect(el!.className).toMatch(/h-\[40px\]/);
+		expect(el!.className).toMatch(/w-\[40px\]/);
+	});
+
+	it('applies size-48 class for size=48', async () => {
+		render(Avatar, { name: 'Herbert Cram', size: 48 });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		expect(el!.className).toMatch(/h-\[48px\]/);
+		expect(el!.className).toMatch(/w-\[48px\]/);
+	});
+
+	it('stacked variant adds -ml-1.5 and ring-2 ring-surface', async () => {
+		render(Avatar, { name: 'Anna Raddatz', size: 26, stacked: true });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		expect(el!.className).toMatch(/-ml-1\.5/);
+		expect(el!.className).toMatch(/ring-2/);
+		expect(el!.className).toMatch(/ring-surface/);
+	});
+
+	it('non-stacked variant does not have -ml-1.5', async () => {
+		render(Avatar, { name: 'Anna Raddatz', size: 26, stacked: false });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		expect(el!.className).not.toMatch(/-ml-1\.5/);
+	});
+
+	it('decorative mode: aria-hidden=true when decorative prop is true', async () => {
+		render(Avatar, { name: 'Anna Raddatz', decorative: true });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		expect(el!.getAttribute('aria-hidden')).toBe('true');
+	});
+
+	it('standalone mode: role=img and aria-label=name when decorative is false', async () => {
+		render(Avatar, { name: 'Herbert Cram', decorative: false });
+		await expect.element(page.getByRole('img', { name: 'Herbert Cram' })).toBeInTheDocument();
+	});
+
+	it('renders overflow +N chip when overflow prop is set', async () => {
+		render(Avatar, { overflow: 3 });
+		await expect.element(page.getByText('+3')).toBeInTheDocument();
+	});
+
+	it('renders placeholder (dashed border) when placeholder prop is true', async () => {
+		render(Avatar, { placeholder: true, size: 26 });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		expect(el!.className).toMatch(/border-dashed/);
+	});
+
+	it('has rounded-full class', async () => {
+		render(Avatar, { name: 'Karl Müller', size: 40 });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		expect(el!.className).toMatch(/rounded-full/);
+	});
+
+	it('stacked variant carries ring classes (dark mode edge on dark surface)', async () => {
+		render(Avatar, { name: 'Karl Müller', size: 26, stacked: true });
+		const el = getAvatar();
+		expect(el).not.toBeNull();
+		// ring-2 ring-surface keeps avatar edges visible on dark surface (#011526)
+		expect(el!.className).toMatch(/ring/);
+	});
+});