Add policy enforcement to prevent runaway crawls and credit burn

This server exposes ~10 tools including recursive crawling, batch scraping, deep research, and browser session control. Several can consume significant API credits or interact with sites in uncontrolled ways:

- `firecrawl_crawl` -- recursive site crawl with no built-in depth/page limit enforcement at the MCP layer
- `firecrawl_deep_research` -- autonomous multi-step research that can chain many API calls
- `firecrawl_batch_scrape` -- bulk operations across many URLs
- Browser session tools -- remote browser control

An agent in a loop calling `firecrawl_crawl` can burn through API credits rapidly.

**Suggestion:** Consider documenting support for [PolicyLayer/Intercept](https://github.com/policylayer/intercept), an open-source MCP proxy that enforces policies on tool calls before execution.

Example policy:

```yaml
version: "1"
default: allow

tools:
firecrawl_crawl:
rules:
- rate_limit: 3/hour

firecrawl_deep_research:
rules:
- action: require_approval

firecrawl_batch_scrape:
rules:
- rate_limit: 5/day
```

One line to set up: `npx -y @policylayer/intercept init`

No documentation file or test is named. Start by locating the server's documentation entry point and reviewing the listed crawl, research, batch-scrape, and browser-session tools; verify the PolicyLayer/Intercept setup command and example policies. Done means the supported integration and its limits are documented clearly without changing tool behavior.

Written by the indexing model from the issue text.