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/lib/shared/api.server.ts

@@ -0,0 +1,25 @@
+/**
+ * Typed API client for the Familienarchiv backend.
+ *
+ * Types are generated from the OpenAPI spec — run `npm run generate:api`
+ * (with the backend running in dev mode) to regenerate src/lib/generated/api.ts.
+ *
+ * Usage in +page.server.ts:
+ *
+ *   export async function load({ fetch }) {
+ *       const api = createApiClient(fetch);
+ *       const { data, error } = await api.GET('/api/documents/{id}', {
+ *           params: { path: { id } }
+ *       });
+ *   }
+ */
+import createClient from 'openapi-fetch';
+import { env } from '$env/dynamic/private';
+import type { paths } from '$lib/generated/api';
+
+export function createApiClient(fetch: typeof globalThis.fetch) {
+	return createClient<paths>({
+		baseUrl: env.API_INTERNAL_URL || 'http://localhost:8080',
+		fetch
+	});
+}