Feature: Support Installation via Homebrew (macOS/Linux)

[GordonBeeming]

Description
To make the tool feel more native on macOS and Linux, we should provide a Homebrew formula. This will allow for better update management and discovery for users who prefer brew over manual script execution.

Acceptance Criteria

• Create a Homebrew formula (likely in a homebrew-tap).
• Ensure brew install gordonbeeming/tap/copilot_here works correctly.
• Verify the installation path integrates correctly with the user's shell.