Add MCP Toplist rank badge

[chrstphe]

Hi! MCP Toplist tracks 81,919 MCP servers across the major
registries, and Snyk is currently ranked #146.

This PR adds a small live badge to your README showing that rank — it updates
automatically as the leaderboard changes:

Totally fine to close if you'd rather not — and if you'd like your server's
data corrected or removed from the leaderboard, just say so here or open an
issue at the site. Thanks for building Snyk!

[CLAassistant]

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[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues

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