Fix broken Smithery badge (returns HTTP 500)

[skillselion]

The Smithery badge in the README is serving HTTP 500, so it renders as a broken image:

https://smithery.ai/badge/@openags/paper-search-mcp   ->  500

This isn't specific to this repo — Smithery's badge endpoint is failing across the ecosystem.

What this PR does: removes that one dead badge line, and offers ours in its place.

[![Listed on Skillselion](https://skillselion.com/badge/mcp/tool/io.github.openags/paper-search-mcp.svg)](https://skillselion.com/mcp/tool/io.github.openags/paper-search-mcp)

We'd be happy to have ours sit there instead — Skillselion is an independent directory of agent skills and MCP servers, and this project is already listed at https://skillselion.com/mcp/tool/io.github.openags/paper-search-mcp whether or not you take the badge.

Entirely your call, and no hard feelings either way:

• Happy for the badge to stay → merge as is.
• Prefer the dead badge just gone → say so and I'll amend this to a removal-only change.
• Prefer nothing touched → close it, no reply needed.

Only the dead Smithery image was changed. Any other badges in your README were left untouched.