Add pdfcheck-mcp and sensormesh-mcp

[jayjex]

Two entries, both on npm and in the official MCP registry.

• app/pdfcheck-mcp.md: @jayjex/pdfcheck-mcp 0.1.1. Validates PDF page-tree structure (pdf_qa for one file, pdf_batch for a directory): /Kids resolve to /Type /Page objects, /Contents points at streams, orphan and /Count checks. stdio, no native deps. Repo: https://github.com/jayjex/pdfcheck-mcp
• app/sensormesh-mcp.md: @jayjex/sensormesh-mcp 0.1.0. Read access to the SensorMesh open IoT sensor data commons: sensor_list, sensor_query with filters, sensor_stats. No API key. Repo: https://github.com/jayjex/sensormesh-mcp

Format follows the frontmatter pattern used by this repo's server entries.