Update site npm dependencies

[Copilot]

Bumps all outdated npm packages in site/ to their latest compatible versions.

Dependencies updated

Production

• gatsby → ^5.16.1 (was ^5.15.0)
• gatsby-plugin-* → ^5.16.0 / ^6.16.0 (were ^5.14.x / ^6.14.x)
• gatsby-remark-* → ^6.16.0 / ^7.16.0 (were ^6.14.x / ^7.14.x)
• react + react-dom → ^19.2.4 (were ^18.3.1; Gatsby 5.16 supports React 19)

Dev

• @testing-library/react → ^16.3.2
• babel-preset-gatsby → ^3.16.0
• prettier → ^3.8.1
• rimraf → ^6.1.3

Constrained

• @mdx-js/react remains at ^2.3.0 (latest v2) — gatsby-plugin-mdx@5.x has a peer dep on @mdx-js/react@^2.0.0, making v3 incompatible.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• unpkg.com
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node scripts/postinstall.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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