Add deep linking for canvas extensions

[jamesmontemagno]

Summary

• Added deep-link support for Canvas Extensions using ?extension=<id>.
• On page load, the matching extension modal opens automatically when the query param is valid.
• If the query param references an unknown extension, it is removed from the URL.

URL state behavior

• Opening an extension now writes extension=<id> to the URL.
• Closing the modal removes the extension query param so shared links stay clean and accurate.

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[Copilot]

Pull request overview

This PR adds URL-based deep linking for Canvas Extension detail modals on the extensions page by syncing the currently open extension to an extension=<id> query parameter. It also auto-opens the referenced extension modal on page load and cleans up the URL when the modal is closed or when an invalid extension ID is provided.

Changes:

• Introduced extension query parameter sync when opening/closing an extension details modal.
• Added page-load behavior to auto-open the extension modal when ?extension=<id> is present and valid.
• Removed invalid extension query parameters from the URL when the ID is unknown.

Show a summary per file

File	Description
website/src/scripts/pages/extensions.ts	Adds deep-link query param synchronization, initial modal open from URL, and a modal close observer to remove the param.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Low

[aaronpowell]

We're overhauling these pages with #2246 which will give them all dedicated URLs, so I'm going to close this