Add an Express.js example to the Connect Gallery

Add a Node.js content example to the Gallery: a small Express.js app demonstrating how to deploy Node.js content to Connect.

Depends on Connect Gallery support for Node.js requirements, shipping in Connect 2026.06, and on this repo's pipeline support for Node.js content (#373).

Work

• Create extensions/express-example/ as simple content: an Express app with a package.json and a manifest.json.
• package.json declares "engines": { "node": ">=22" }, the floor for the latest Express. This is what Connect uses to select a Node installation at build and run time, and what the release automation publishes as the Gallery requirement.
• The manifest needs the standard extension section (name, title, description, homepage, category: "example", tags, minimumConnectVersion).
• Set minimumConnectVersion to 2026.06.0, the release shipping Node.js general availability and Gallery support for Node.js requirements. This is what keeps older Connect UIs, which ignore the unknown nodejs key, from offering a doomed install.
• Add tags (likely nodejs, javascript, express) to extensions.json; new tags need review per the contributing guide.
• Add a README.md for the Gallery homepage link.
• Register the path filter in .github/workflows/extensions.yml (simple-extension-changes).

Release timing

Keep version: "0.0.0" (no release) until Connect 2026.06 ships with Gallery support for Node.js requirements. Node.js content support is generally available in the same release.