[CI] Add batch_export_page MCP tool

[egdev6]

Summary

Add an MCP tool that exports all relevant boards from a Penpot page in one operation so component references can be attached to GitHub Projects tasks without repetitive manual exports.

Scope

• accept pageName
• support optional boardNamePattern
• export png or svg
• support optional saveToDirectory
• return metadata for every exported board

Acceptance Criteria

• exports all top-level boards from 01 Button
• can export only a filtered subset
• returns boardId, boardName, filePath, width, and height

Tasks

• implement BatchExportPageTool.ts
• define input/output schema
• locate top-level boards from the target page
• integrate per-board export
• add consistent file naming
• support optional saving to disk
• register the tool in PenpotMcpServer.ts
• add tests with a bridge mock
• document usage examples

Additional notes

This is the first tool that directly produces contributor-facing artifacts.