Merge gh install into publish step for same-process PATH

[Finesssee]

Summary

• merge the GitHub CLI install step into the publish step's command block so they share the same PowerShell process
• the previous approach (separate run steps) failed because CircleCI runs each run step as a separate shell process — PATH changes in one step do not propagate to the next
• within a single run step, child processes (including the spawned powershell.exe for publish-github-release.ps1) inherit the parent's $env:Path

Root cause

Pipelines #38 and #39: gh was installed in a separate run step and the directory was added to PATH, but the publish run step started a new shell that did not inherit the PATH change.

Validation

• circleci config validate passed
• no version files changed

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