Initial commit: AI-driven visual novel scaffold

- Monorepo (pnpm workspace): apps/web + packages/{types,ai-client,engine}
- Next.js 16 web app with three-stage AI orchestration
- Three independently configurable providers: text LLM, image generator, vision model
- Warm minimalist editorial UI design
- One-click Vercel deploy ready

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

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

@@ -0,0 +1,32 @@
+import { startSession } from "@dada/engine";
+import type { StartRequest } from "@dada/types";
+import { NextResponse } from "next/server";
+import { loadEngineConfig } from "@/lib/config";
+
+export const runtime = "nodejs";
+export const maxDuration = 60;
+
+export async function POST(req: Request) {
+  let body: StartRequest;
+  try {
+    body = (await req.json()) as StartRequest;
+  } catch {
+    return NextResponse.json({ error: "Invalid JSON" }, { status: 400 });
+  }
+
+  if (!body.worldSetting?.trim() || !body.styleGuide?.trim()) {
+    return NextResponse.json(
+      { error: "worldSetting and styleGuide are required" },
+      { status: 400 },
+    );
+  }
+
+  try {
+    const config = loadEngineConfig();
+    const result = await startSession(config, body);
+    return NextResponse.json(result);
+  } catch (err) {
+    const message = err instanceof Error ? err.message : "Unknown error";
+    return NextResponse.json({ error: message }, { status: 500 });
+  }
+}