feat(workbench): support FDC3 event listeners

[akira-in-tech]

Describe your change

Add FDC3 2.2 event support to the Workbench while preserving compatibility with FDC3 2.0 and 2.1 implementations.

• Listen for userChannelChanged events and keep the displayed current user channel in sync.
• Use PrivateChannel.addEventListener for addContextListener, unsubscribe, and disconnect events on FDC3 2.2 and later.
• Retain the legacy Private Channel callbacks for FDC3 2.0 and 2.1.
• Preserve event details.contextType in logs and event history, and broadcast only contexts that match the registered listener type.
• Add event status, history, and copyable examples to the relevant Workbench tabs.
• Add Vitest coverage and a CHANGELOG entry.

Related Issue

Resolves #1674

Contributor License Agreement

• I acknowledge that a contributor license agreement is required and that I have one in place or will seek to put one in place ASAP.

Impact

The change is limited to the FDC3 Workbench. It does not modify the FDC3 API, schemas, conformance tests, context types, or intents.

Validation

• npm run test --workspace fdc3-workbench: 7 tests passed
• npm run build --workspace fdc3-workbench: passed
• npm run lint --workspace fdc3-workbench: passed with 0 errors
• npm test: passed for all workspaces
• npm run lint: passed for all workspaces

[netlify]

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[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: akira-in-tech / name: akira (71b10b6)

[akira-in-tech]

Synced the branch with the latest main in 7784423 to pick up the current website/build dependency baseline. The Netlify deploy preview is now green and returns HTTP 200. I also revalidated the Workbench with Node 24.18.0/npm 11.16.0: 9 tests pass, the production build passes, and lint reports 0 errors.