docs: README only lists the unified MCP tools, omits vault/track/growth/fleet sub-MCPs

[BryanFRD]

Problem

README.md documents one binary (@ferrlabs/mcp) and an "Available Tools" table of 12 tools, plus a note that FerrFlow CLI tools were removed in v4.0.0. But the repo now ships five additional MCP servers as separate packages:

• @ferrlabs/mcp-vault — vaults, vault-details, secrets, secret-mutations (create/update/delete/rotate/archive), audit
• @ferrlabs/mcp-track — issues, issue-details, comments, cycles, milestones, projects, search
• @ferrlabs/mcp-growth — sites, pages, forms, releases, analytics, seo
• @ferrlabs/mcp-fleet — agents (incl. trigger_agent_run), runs

None of these packages, their tools, their install/config, or their per-product base-URL env vars (FERRFLEET_API_URL, FERRGROWTH_API_URL, FerrTrack base) appear in the README. The "Stack" section and the smoke-test sample output still reference 4.0.0, while packages are at 5.2.5 / 6.0.0.

Why it matters

Users can't discover or configure the sub-MCPs from the docs, and the destructive tools they expose are entirely undocumented. The README is the published face on npm and the marketing-site source of truth per repo conventions.

Proposed approach

• Add an "MCP servers" section describing each package, its npm name, and its mcpServers config snippet.
• Document each package's tool table (mark destructive tools clearly).
• Document the per-product base-URL env overrides.
• Refresh stale 4.0.0 references in "Stack" and the smoke-test sample output.

Acceptance criteria

• README lists all five MCP packages with install/config and tool tables.
• Destructive tools are flagged.
• Per-product env vars are documented.
• No lingering 4.0.0 placeholders that contradict shipped versions.