Stop the Server README from installing a stale CLI prerelease

[rmcdaniel]

Problem

The Server README active CLI installation example pins 2.0.0-rc.5 while the current published CLI release candidate is 2.0.0-rc.12. Removing the pin is not sufficient during prerelease because the installer latest channel resolves to the latest stable 0.x release.

A first-time evaluator following the Server README can therefore install an obsolete 2.0 client or silently leave the 2.0 train.

Acceptance criteria

• Make the Server README install the intended current or explicitly qualified 2.0 CLI release with an exact generated pin.
• Derive the pin from a versioned public release handoff or other single authority instead of a manually maintained literal.
• Preserve the installer latest behavior for stable channels.
• Verify the referenced release assets and show that the installed binary reports the expected version.
• Add structural drift coverage without coupling ordinary README prose to tests.

Delete when

Delete when the public Server README installs the intended 2.0 CLI artifact and release advancement cannot leave that active command on an old prerelease.