docs: remove free tier, update rate limits and auth for demo+pro model

- Remove free tier from rate limits, add Demo (5/hour, watermarked)
- Update auth section: remove free-tier key mention, link to docfast.dev
- Update getting started: demo → upgrade to Pro → use API key
- Add deprecated: true to /v1/signup/free swagger annotation
- Regenerate openapi.json

src/index.ts

@@ -104,6 +104,7 @@ app.use("/v1/demo", express.json({ limit: "50kb" }), pdfRateLimitMiddleware, dem
  * /v1/signup/free:
  *   post:
  *     tags: [Account]
+ *     deprecated: true
  *     summary: Request a free API key (discontinued)
  *     description: Free accounts have been discontinued. Use the demo endpoints or upgrade to Pro.
  *     responses:

src/swagger.ts

@@ -11,7 +11,7 @@ const options: swaggerJsdoc.Options = {
       title: "DocFast API",
       version,
       description:
-        "Convert HTML, Markdown, and URLs to pixel-perfect PDFs. Built-in invoice & receipt templates.\n\n## Authentication\nAll conversion and template endpoints require an API key via `Authorization: Bearer <key>` or `X-API-Key: <key>` header.\n\n## Rate Limits\n- Free tier: 100 PDFs/month, 10 req/min\n- Pro tier: 5,000 PDFs/month, 30 req/min\n\n## Getting Started\n1. Try the demo endpoints (no auth required, 5/hour limit)\n2. Upgrade to Pro at [docfast.dev](https://docfast.dev)\n3. Use your API key to convert documents",
+        "Convert HTML, Markdown, and URLs to pixel-perfect PDFs. Built-in invoice & receipt templates.\n\n## Authentication\nAll conversion endpoints require an API key via `Authorization: Bearer <key>` or `X-API-Key: <key>` header. Get your key at [docfast.dev](https://docfast.dev).\n\n## Rate Limits\n- Demo: 5 conversions/hour, watermarked output\n- Pro tier: 5,000 PDFs/month, 30 req/min\n\n## Getting Started\n1. Try the demo endpoints (no auth required, 5/hour limit)\n2. Upgrade to Pro at [docfast.dev](https://docfast.dev) for clean output and higher limits\n3. Use your API key to convert documents",
       contact: {
         name: "DocFast",
         url: "https://docfast.dev",