feat: add OpenAPI spec (dev only) with typed frontend client

- Add springdoc-openapi 3.0.2 (supports Spring Boot 4) to backend
- Disable api-docs/swagger-ui in application.yaml (prod default)
- Enable both in application-dev.yaml; Swagger UI at /swagger-ui.html
- Add openapi-fetch (runtime) and openapi-typescript (dev) to frontend
- Add generate:api npm script — run with backend up to regenerate types
- Add src/lib/api.server.ts typed client factory (uses SvelteKit fetch)
- Gitignore src/lib/generated/api.ts (generated artifact)

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

frontend/src/lib/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
+    });
+}