feat(brave-search): Make rate limits configurable via environment variables

Summary

The brave-search server (now in servers-archived) has hardcoded rate limits that don't match Brave Search API tier limits. This artificially throttles users with paid plans.

Problem

// Current hardcoded limits
const RATE_LIMIT = {
  perSecond: 1,
  perMonth: 15000
};

Users with Base ($5/mo) or Pro plans are artificially throttled to Free tier limits.

Proposed Solution

Make rate limits configurable via environment variables with backward-compatible defaults:

const RATE_LIMIT = {
  perSecond: parseInt(process.env.BRAVE_RATE_LIMIT_PER_SECOND || '1', 10),
  perMonth: parseInt(process.env.BRAVE_RATE_LIMIT_PER_MONTH || '15000', 10)
};

Benefits:

• Zero breaking changes (defaults match current behaviour)
• Users can configure based on their actual API tier
• Simple 2-line change

Example Configuration

{
  "mcpServers": {
    "brave-search": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-brave-search"],
      "env": {
        "BRAVE_API_KEY": "your-key",
        "BRAVE_RATE_LIMIT_PER_SECOND": "20"
      }
    }
  }
}

Note

I understand brave-search was moved to servers-archived (which is read-only). I'm happy to submit a PR if you can advise the best path forward - whether that's:

1. Unarchiving just for this fix
2. Bringing brave-search back to this repo
3. Another approach

The fix is minimal and backward-compatible.

Start by locating the archived brave-search server and its RATE_LIMIT definition; the issue does not name a file or test. Confirm where this change could be made given that servers-archived is read-only, then verify that omitted environment variables preserve the current limits and configured values are applied.