docs: add a tags column for community tools

[whoalin1]

Refs fastify#3618

Summary

• Converts the Community Tools section of docs/Guides/Ecosystem.md into a table with a lowercase tags column.
• Leaves the Core and Community sections as alphabetical lists. Descriptions and links are unchanged.
• Updates the ecosystem order check so table rows stay alphabetical, and so tags stay lowercase, comma-separated, and sorted.

This is a first slice of fastify#3618, limited to the shortest section. It follows the review on fastify#6518: keep the current order and add a tags column, instead of introducing category headings. fastify#4938 settled on the same shape, with lowercase tags.

Website follow-up

fastify/website scripts/build-plugin-list.mjs only reads markdown list items. After this change, the seven Community Tools entries drop out of plugins.json until that script reads table rows. Core and Community are unchanged, so the rest of the ecosystem page is unaffected. The guide page itself renders the table.

Test plan

• node --test test/scripts/lint-ecosystem.test.js
• The new test covers list order, table order, tag format, and the checked-in guide
• npm run lint:markdown (tables are exempt from the line-length rule)