Add rate limit headers to OpenAPI generation script

- Update generate-openapi.mjs to include header components
- Ensure public/openapi.json has rate limit headers
- Update rate limits description in generation script

public/openapi.json

@@ -3,7 +3,7 @@
   "info": {
     "title": "DocFast API",
     "version": "1.0.0",
-    "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## Demo Endpoints\nTry the API without signing up! Demo endpoints are public (no API key needed) but rate-limited to 5 requests/hour per IP and produce watermarked PDFs.\n\n## Rate Limits\n- Demo: 5 PDFs/hour per IP (watermarked)\n- Pro tier: 5,000 PDFs/month, 30 req/min\n\n## Getting Started\n1. Try the demo at `POST /v1/demo/html` — no signup needed\n2. Subscribe to Pro at [docfast.dev](https://docfast.dev/#pricing) for clean PDFs\n3. Use your API key to convert documents",
+    "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## Demo Endpoints\nTry the API without signing up! Demo endpoints are public (no API key needed) but rate-limited to 5 requests/hour per IP and produce watermarked PDFs.\n\n## Rate Limits\n- Demo: 5 PDFs/hour per IP (watermarked)\n- Pro tier: 5,000 PDFs/month, 30 req/min\n\nAll rate-limited endpoints return `X-RateLimit-Limit`, `X-RateLimit-Remaining`, and `X-RateLimit-Reset` headers. On `429`, a `Retry-After` header indicates seconds until the next allowed request.\n\n## Getting Started\n1. Try the demo at `POST /v1/demo/html` — no signup needed\n2. Subscribe to Pro at [docfast.dev](https://docfast.dev/#pricing) for clean PDFs\n3. Use your API key to convert documents",
     "contact": {
       "name": "DocFast",
       "url": "https://docfast.dev",
@@ -56,6 +56,36 @@
         "description": "API key via X-API-Key header"
       }
     },
+    "headers": {
+      "X-RateLimit-Limit": {
+        "description": "The maximum number of requests allowed in the current time window",
+        "schema": {
+          "type": "integer",
+          "example": 30
+        }
+      },
+      "X-RateLimit-Remaining": {
+        "description": "The number of requests remaining in the current time window",
+        "schema": {
+          "type": "integer",
+          "example": 29
+        }
+      },
+      "X-RateLimit-Reset": {
+        "description": "Unix timestamp (seconds since epoch) when the rate limit window resets",
+        "schema": {
+          "type": "integer",
+          "example": 1679875200
+        }
+      },
+      "Retry-After": {
+        "description": "Number of seconds to wait before retrying the request (returned on 429 responses)",
+        "schema": {
+          "type": "integer",
+          "example": 60
+        }
+      }
+    },
     "schemas": {
       "PdfOptions": {
         "type": "object",