[DOC] update download page for 26.06 release [skip ci]

[nvliyuan]

Description

This PR updates the download and archive documentation for the v26.06.0 release.

Changes include:

• Update docs/download.md to list v26.06.0 artifacts, Maven coordinates, signature verification commands, and concise release notes.
• Move the previous current release, v26.04.2, into docs/archive.md as the newest archived release.
• Verify the Spark support matrix against pom.xml on release/26.06.
• Update the Dataproc Serverless runtime list against the spark-rapids-tme/documentation update-managed-spark-docs branch.

Validation:

• git diff --check -- docs/download.md docs/archive.md
• IDE lints for docs/download.md and docs/archive.md

Checklists

Documentation

• Updated for new or modified user-facing features or behaviors
• No user-facing change

Testing

• Added or modified tests to cover new code paths
• Covered by existing tests
  (Please provide the names of the existing tests in the PR description.)
• Not required

Performance

• Tests ran and results are added in the PR description
• Issue filed with a link in the PR description
• Not required

[greptile-apps]

Greptile Summary

This PR updates the download and archive pages for the v26.06.0 release of the RAPIDS Accelerator for Apache Spark. docs/download.md is updated to reflect the new release artifacts, Maven coordinates, signature commands, Dataproc Serverless runtime list, and release notes, while the previous release (v26.04.2) is moved into docs/archive.md.

• docs/download.md: Version bumped from v26.04.2 → v26.06.0 throughout; Dataproc Serverless runtimes refreshed to 1.2 LTS, 2.2 LTS, 2.3 LTS, and 3.0; comprehensive new release notes covering Delta Lake, Iceberg, GPU expression, and correctness improvements.
• docs/archive.md: Full v26.04.2 release block (CUDA 12 + 13, x86_64 + arm64 tables, verify-signature steps, hotfix release notes) prepended as the newest archived entry.

Confidence Score: 5/5

Pure documentation update — no code paths are touched, only Markdown content in two release-page files is changed.

Both files contain only prose and table markup. All version strings, Maven coordinates, and artifact URLs are internally consistent for v26.06.0, and the v26.04.2 archive block faithfully copies the content that was previously in download.md. There are no code, configuration, or build-system changes to introduce regressions.

No files require special attention.

Important Files Changed

Filename	Overview
docs/download.md	Updated current release from v26.04.2 to v26.06.0; all artifact URLs, Maven coordinates, signature commands, and release notes updated; Dataproc Serverless runtime list refreshed to 1.2 LTS / 2.2 LTS / 2.3 LTS / 3.0
docs/archive.md	v26.04.2 block prepended at the top of the archive, including hardware requirements, download table (CUDA 12 + 13, x86_64 + arm64), Maven coordinates, and release notes; content mirrors what was previously in download.md

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[PR: v26.06.0 release doc update] --> B[docs/download.md]
    A --> C[docs/archive.md]
    B --> D[Current release: v26.06.0]
    D --> D1[CUDA 12 artifacts\nx86_64 + arm64\nScala 2.12 + 2.13]
    D --> D2[CUDA 13 artifacts\nx86_64 + arm64\nScala 2.12 + 2.13]
    D --> D3[Dataproc Serverless\n1.2 LTS / 2.2 LTS / 2.3 LTS / 3.0]
    D --> D4[Release notes\nDelta Lake, Iceberg, GPU expressions, correctness fixes]
    C --> E[Prepended: v26.04.2 archive block]
    E --> E1[CUDA 12 + 13 tables\nx86_64 + arm64]
    E --> E2[Hotfix release notes\nv26.04.2 / v26.04.1 / v26.04.0]

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_{Reviews (2): Last reviewed commit: "[DOC] update Dataproc Serverless release..." | Re-trigger Greptile}

[NvTimLiu]

LGTM, +1

[nvliyuan]

build