Add PowMCP Ebook File Check hosted MCP server

[adam-paulin]

Summary

Adds PowMCP Ebook File Check to Developer Productivity & Utilities, following the README’s one-category-bullet contribution route. This is a different app from the already-listed SSL Certificate Check; that entry is unchanged.

• Product/docs: https://powmcp.com/apps/epub-check/
• Hosted Streamable HTTP endpoint: https://powmcp.com/epub-check/mcp
• Tools: ebook_check and ebook_compare, backed by EPUBCheck.
• Guest access has usage limits; optional account linking uses OAuth.
• Contact: support@powmcp.com; PowMCP is a product of Frostwave Labs Inc.

The description explicitly excludes visual rendering, accessibility assessment, and guaranteed bookstore acceptance. This is a hosted proprietary service; no claim that its implementation is open source.

Verification

• Searched category files, sidecars, and existing issues/PRs for the project name and epub-check URL; no duplicate found.
• Live MCP initialization succeeded on September 10, 2026 and reported epub-check 0.5.3 with these tool instructions.
• Product documentation resolves successfully.
• git diff --check passed; only one category Markdown file changed.
• Generated catalog/profile files were intentionally left to the upstream indexer.

Submitted from the PowMCP-owned contribution fork for ongoing maintenance.