Route more commands to brew-rs

[MikeMcQuaid]

• Enable autoremove, cleanup, outdated and postinstall in the Rust frontend gate.
• Keep update on the shell path so Homebrew's update flow still drives update-report.

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[Copilot]

Pull request overview

This PR expands the set of brew subcommands that are eligible to be executed via the experimental brew-rs Rust frontend (when the existing gating conditions are met), while leaving update on the shell-based path as described.

Changes:

• Route autoremove, cleanup, outdated, and postinstall through the Rust frontend gate.
• Preserve the existing command-routing behavior for other commands (including update remaining outside the Rust gate).

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