Add Deploy 17.2.0-rc1, 18.0.0-rc1 and 18.0.0-rc2 release notes

[ronaldbarendse]

📋 Description

Adds release notes for Umbraco Deploy 17.2.0-rc1, 18.0.0-rc1, and 18.0.0-rc2.

17.2.0-rc1 ships short-term fixes for running Deploy on load-balanced backoffice setups: ARRAffinity cookie preservation, a cluster-wide worker lock to prevent concurrent deploys, and single-node disk-trigger processing.

18.0.0-rc1 provides Umbraco CMS 18 compatibility and is the first major Deploy release for v18. Highlights:

• Support for transferring, restoring, importing, and exporting Elements (publishable, versioned content items in the new Library section).
• Import-time migration of Nested Content (with MaxItems = 1) and single-block-mode Block List configurations to the new Umbraco.SingleBlock editor.
• Major UI/UX overhaul of the backoffice Deploy experience — new workspace launched from the environment header app, redesigned modals, refreshed schema and configuration views, and a cleaner integration surface for extension developers.
• The load-balancing improvements introduced in 17.2.0-rc1 are also included.

18.0.0-rc2 restricts Deploy SignalR hubs to WebSockets when the Umbraco:CMS:SignalR:ClientShouldSkipNegotiation CMS setting is enabled, aligning Deploy with the v18 SignalR contract.

📎 Related Issues (if applicable)

N/A

✅ Contributor Checklist

I've followed the Umbraco Documentation Style Guide and can confirm that:

• Code blocks are correctly formatted.
• Sentences are short and clear (preferably under 25 words).
• Passive voice and first-person language ("we", "I") are avoided.
• Relevant pages are linked.
• All links work and point to the correct resources.
• Screenshots or diagrams are included if useful.
• Any code examples or instructions have been tested.
• Typos, broken links, and broken images are fixed.

Product & Version (if relevant)

Umbraco Deploy 17.2.0-rc1, 18.0.0-rc1, and 18.0.0-rc2.

Deadline (if relevant)

These versions are already available, so as soon as possible!

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[Copilot]

Pull request overview

This PR adds release notes entries for recent Umbraco Deploy release candidates in the v17 and v18 documentation, reflecting load-balancing fixes and v18 compatibility/UX changes.

Changes:

• Add release notes for Deploy 17.2.0-rc1 (load-balancing/worker lock/disk trigger behavior).
• Add release notes for Deploy 18.0.0-rc1 (CMS 18 compatibility, UX refresh summary, migration notes, load-balancing improvements).
• Add release notes for Deploy 18.0.0-rc2 (SignalR WebSockets-only behavior when skip negotiation is enabled).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
18/umbraco-deploy/release-notes.md	Adds 18.0.0-rc1/rc2 release notes plus a “Backoffice UX refresh” subsection.
17/umbraco-deploy/release-notes.md	Adds 17.2.0-rc1 release notes focused on load-balanced backoffice fixes.

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