Repair MCP surface documentation

Constraint: Keep the MCP tool surface light; do not restore deprecated browser tools or invent batch MCP tools.
Rejected: Add batch/browser MCP docs back | they would misrepresent or grow the agent surface instead of documenting current tools.
Confidence: high
Scope-risk: narrow
Directive: Defer package version changes to the release/merge process.
Tested: git diff --check; grep for removed stale MCP/env symbols; npm run build; npm test
Not-tested: Runtime calls against Firecrawl API; this PR changes README guidance and one tool-description string only.

Author: hmishra2250