feat: Vercel Hobby deploy readiness — image URLs, jsonrepair, DeepSeek

- Move vercel.json to apps/web/ with correct route paths; cap scene route
  maxDuration 120→60s for Hobby. Root vercel.json removed. Vercel project's
  Root Directory must be set to apps/web (Deploy button URL passes this).
- Switch image transport from base64-in-JSON to Runware-hosted URLs:
  generateImage now uses outputType=URL and returns {imageUrl, imageUuid};
  StartResponse/SceneResponse carry imageUrl; VisionRequest carries
  prevImageUrl (server re-fetches the bytes for click annotation). This
  eliminates the 4.5MB serverless body-size risk.
- Painter and director prefer URL over UUID for referenceImages — the UUID
  returned by Runware imageInference isn't always recognized in the refs
  pipeline (surfaces as `failedToTransferImage`).
- Client preloads scene images via `new Image().decode()` before committing
  to React state, so URL transitions render instantly; prefetched scenes
  also warm the HTTP cache.
- jsonParser uses the jsonrepair package (replaces hand-rolled repair) and
  adds a targeted preRepair regex for the missing-key-close-quote pattern
  that jsonrepair couldn't disambiguate. Full raw model output dumped on
  failure for diagnostic visibility.
- Default text provider switched to DeepSeek v4-flash via direct API
  (significantly more stable JSON than MiMo v2.5-pro). VISION/TTS stay on
  MiMo (DeepSeek has no multimodal / TTS offerings).
- next.config: drop dead experimental.serverActions.bodySizeLimit (no
  server actions used).
- README: real Deploy button URL (zonghaoyuan/yume + root-directory=apps/web
  + TTS/MOCK_IMAGE in env list); refreshed env vars table with optional
  TTS section.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/app/api/scene/route.ts

@@ -4,7 +4,11 @@ import { NextResponse } from "next/server";
 import { loadEngineConfig } from "@/lib/config";
 
 export const runtime = "nodejs";
-export const maxDuration = 120;
+// 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;