feat(mcp): lint_page_html tool

[aram-devdocs]

Summary

Accept inline HTML + base URL; lint without requiring a real
URL. Useful for agents testing generated components before save.

Crate / area

plumb-mcp — rmcp-based stdio MCP server

Phase / batch

Part of #65 → Batch 7C (MCP V1 — new tools + HTTP transport).

Effort: M

PRD references

• PRD §14.2

Acceptance criteria

• Tool registered; protocol test.
• Response cap matches lint_url.

Dependencies

• None (first in batch; batch-level deps gate this).

Review gates

• 02-spec-reviewer
• 03-code-quality-reviewer
• 05-architecture-validator
• 04-test-runner
• 06-security-auditor

How to deliver

Dispatch /gh-issue <this-issue-number>. See the root AGENTS.md and the scoped plumb-mcp/AGENTS.md for the invariants that apply.

Suggested delivery: gh-issue