fix(web): remove hardcoded maxDuration so Vercel dashboard setting takes effect

Code-level `export const maxDuration = 60` and vercel.json `functions`
block were overriding the dashboard's 300s setting, causing ~100 504
timeouts per day on /api/scene and /api/start. Removing them lets each
Vercel plan use its own default (60s Hobby, 300s Pro) without breaking
self-deployers.

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

app/api/scene/route.ts

@@ -13,11 +13,6 @@ function stripKnownVoices(
 }
 
 export const runtime = "nodejs";
-// Capped at 60 for Vercel Hobby (300 allowed on Pro). The scene pipeline is
-// Writer + CharDesigner×N + Cinematographer + Painter — happy path 9–12s; the
-// tail (cold provider, multiple new characters) can push 30–45s, so 60 is a
-// reasonable headroom on Hobby.
-export const maxDuration = 60;
 
 export async function POST(req: Request) {
   let body: SceneRequest;