refactor: move lib-root files to lib/shared/ and finalize domain structure

- Move api.server.ts, errors.ts, types.ts, utils.ts, relativeTime.ts to lib/shared/
- Move person relationship components to lib/person/relationship/
- Move Stammbaum components to lib/person/genealogy/
- Move HelpPopover to lib/shared/primitives/
- Update all import paths across routes, specs, and lib files
- Update vi.mock() paths in server-project test files
- Remove now-empty legacy directories (components/, hooks/, server/, etc.)
- Update vite.config.ts coverage include paths for new structure
- Update frontend/CLAUDE.md to reflect domain-based lib/ layout

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

frontend/src/routes/briefwechsel/+page.server.ts

@@ -1,7 +1,7 @@
 import { error } from '@sveltejs/kit';
 import type { components } from '$lib/generated/api';
-import { createApiClient } from '$lib/api.server';
-import { getErrorMessage } from '$lib/errors';
+import { createApiClient } from '$lib/shared/api.server';
+import { getErrorMessage } from '$lib/shared/errors';
 
 export async function load({ url, fetch, locals }) {
 	const senderId = url.searchParams.get('senderId') || '';

frontend/src/routes/briefwechsel/page.server.spec.ts

@@ -1,10 +1,12 @@
 import { describe, expect, it, vi, beforeEach } from 'vitest';
 import { load } from './+page.server';
 
-vi.mock('$lib/api.server', () => ({ createApiClient: vi.fn() }));
-vi.mock('$lib/errors', () => ({ getErrorMessage: (code: string) => code ?? 'Unknown error' }));
+vi.mock('$lib/shared/api.server', () => ({ createApiClient: vi.fn() }));
+vi.mock('$lib/shared/errors', () => ({
+	getErrorMessage: (code: string) => code ?? 'Unknown error'
+}));
 
-import { createApiClient } from '$lib/api.server';
+import { createApiClient } from '$lib/shared/api.server';
 
 const writeUser = { groups: [{ permissions: ['WRITE_ALL'] }] };
 const readUser = { groups: [{ permissions: ['READ_ALL'] }] };