[CI] Add component_structure_report MCP tool

[egdev6]

Summary

Add an MCP diagnostic tool that evaluates whether a component page is actually useful as a contributor reference, reporting visible coverage, organization signals, and missing states or gaps.

Scope

• inspect top-level boards
• infer minimal signals:
  • variants
  • light/dark comparison
  • states
  • naming quality
  • screenshot readiness
• return gaps and a short summary

Acceptance Criteria

• correctly detects partial coverage on 01 Button
• reports missing states when they are not explicitly present
• returns a short operational summary for contributors

Tasks

• implement ComponentStructureReportTool.ts
• define input/output schema
• inspect board names and relevant child names
• implement signals (hasVariantCoverage, hasStateCoverage, etc.)
• implement gaps list
• generate a concise summary
• register the tool in PenpotMcpServer.ts
• add tests with a bridge mock
• document usage examples

Additional notes

The tool must not invent states or coverage that are not explicitly represented in the source material.