Add Ubuntu 26.04 (Resolute) images for .NET 10 and promote to supported

[Copilot]

• Switch Resolute from pre-release/preview to supported in tests by removing IsUnstable: true from OS.cs
• Add .NET 10 Resolute images (Dockerfiles, manifest.json, test data, READMEs) using the image-manager custom agent
• Add .NET 10 Resolute test data entries in TestData.cs
• Regenerate internal Dockerfile baselines for 10.0 resolute (fixed to use scrubbed versions, staging URLs, ACCESSTOKEN auth)
• Run code review (no issues found)
• CodeQL security check (timed out - no executable code changes)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add Ubuntu 26.04 (Resolute Raccoon) images</issue_title>
<issue_description>Ubuntu 26.04 LTS "Resolute Raccoon" is scheduled to release on April 23, 2026.

Per our supported platforms policy, when new Ubuntu LTS versions are released, images are added for the latest .NET version and the latest LTS .NET version (if they differ). At the time of Ubuntu 26.04's release, .NET 10 will be both the latest released version and the latest LTS, so:

• Add resolute images for .NET 10
• Do nothing for .NET 8 or .NET 9
• Ship only resolute (for Ubuntu) for .NET 11 when it releases

.NET 11 preview images based on resolute are already available in the nightly repos.</issue_description>

<agent_instructions>Make sure that we switch Resolute from pre-release/preview to supported in the tests, so that we run the full test suite.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@richlander Sounds good. Can we do same day release for resolute like we did for noble? I can do a blog post. @lbussell Since Resolute images are opt-in for .NET 10, I think we can ship them early, on April Patch Tuesday (2026-04-14).

• Fixes Add Ubuntu 26.04 (Resolute Raccoon) images #7094

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[lbussell]

@copilot internal dockerfile baselines need to be regenerated.

[Copilot]

@copilot internal dockerfile baselines need to be regenerated.

Regenerated the internal Dockerfile baselines for 10.0 resolute in 756064a. They were previously containing public Dockerfile content (real versions, public URLs) instead of the proper internal format (scrubbed 0.0.0 versions, dotnetstage.blob.core.windows.net staging URLs, ACCESSTOKEN auth, placeholder hashes).

[lbussell]

Should we put Resolute above Noble in tag listings for .NET 10?

I guess the question I'm asking is, should the default platform be listed before the latest platform? Even if the default platform is still supported?

For reference, we did put Bookworm above Bullseye for .NET 6 and 7: https://github.com/dotnet/dotnet-docker/pull/4670/changes

@richlander

[lbussell]

Wrong target branch, will cherry-pick and open another PR in order to avoid mass notification spam from switching between branches.

[lbussell]

Superseded by #7107