fix: correct image URL path to match API route

Changed from /api/zine/[id]/image/p1.png to /api/zine/[id]?image=p1
to match the actual API route handler.

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

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

web/app/api/generate-page/route.ts

@@ -60,7 +60,7 @@ export async function POST(request: NextRequest) {
 
     return NextResponse.json({
       pageNumber,
-      imageUrl: `/api/zine/${zineId}/image/p${pageNumber}.png`,
+      imageUrl: `/api/zine/${zineId}?image=p${pageNumber}`,
       success: true,
     });
   } catch (error) {