Add Ubuntu 26.04 to CI and package builds.

[Ferroin]

Summary

Expected release date is 2026-04-23.

Test Plan

CI passes on this PR.

Additional Info

Relevant to #21912

---

Summary by cubic

Add Ubuntu 26.04 as the default Ubuntu target in CI and package builds, and document support. Prepares for the 2026-04-23 Ubuntu release.

• New Features
  • CI/builds: switch default Ubuntu to 26.04 with ubuntu/resolute; keep 24.04 as an explicit target with ubuntu/noble.
  • Docs: add Ubuntu 26.04 to PLATFORM_SUPPORT.

^{Written for commit fdbfbaa. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

Architecture diagram

sequenceDiagram
    participant GHA as GitHub Actions CI
    participant Matrix as Matrix Job Generator
    participant Runner as Build Runner (Ubuntu)
    participant Repo as Package Repository

    Note over GHA,Repo: CI Build & Packaging Flow (Updated for Ubuntu 26.04)

    GHA->>Matrix: Load .github/data/distros.yml
    
    rect rgb(23, 37, 84)
    Note right of Matrix: CHANGED: 26.04 (Resolute) is now the default anchor
    Matrix->>Runner: Initialize job (distro: ubuntu, version: 26.04)
    Runner->>Runner: Run build scripts
    Runner->>Repo: CHANGED: Push packages to 'ubuntu/resolute'
    end

    rect rgb(5, 46, 22)
    Note right of Matrix: NEW: 24.04 (Noble) added as explicit secondary target
    Matrix->>Runner: Initialize job (distro: ubuntu, version: 24.04)
    Runner->>Runner: Run build scripts
    Runner->>Repo: Push packages to 'ubuntu/noble'
    end

    Note over GHA,Repo: Documentation update: PLATFORM_SUPPORT.md now reflects 26.04 availability

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[thiagoftsm]

CI passed with success.