Fix FetchFn type compatibility for CI

Make FetchFn accept both HttpResponse and Response types to fix
TypeScript errors in CI where Bun's Response type is stricter.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ndbroadbent

src/search/openlibrary.ts

@@ -14,9 +14,9 @@ import { DEFAULT_TIMEOUT, DEFAULT_USER_AGENT } from './types'
 const SEARCH_API = 'https://openlibrary.org/search.json'
 
 /**
- * Fetch function type that returns HttpResponse.
+ * Fetch function type - compatible with both HttpResponse and standard Response.
  */
-type FetchFn = (url: string, init?: RequestInit) => Promise<HttpResponse>
+type FetchFn = (url: string, init?: RequestInit) => Promise<HttpResponse | Response>
 
 /**
  * Configuration for Open Library search.

src/search/wikidata.ts

@@ -20,9 +20,9 @@ import {
 const SPARQL_ENDPOINT = 'https://query.wikidata.org/sparql'
 
 /**
- * Fetch function type that returns HttpResponse.
+ * Fetch function type - compatible with both HttpResponse and standard Response.
  */
-type FetchFn = (url: string, init?: RequestInit) => Promise<HttpResponse>
+type FetchFn = (url: string, init?: RequestInit) => Promise<HttpResponse | Response>
 
 /**
  * Configuration for Wikidata search.