#7489: feat: add brew to Dockerfile

This PR addresses #6065 and adding `Brew` installation step into Dockerfile. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> Adds a Homebrew installation into the runtime image by copying the `/home/linuxbrew/.linuxbrew` prefix from `homebrew/brew:4.6.20`, adjusting ownership before switching to the non-root `node` user, and prepending Homebrew’s `bin/` and `sbin/` to `PATH`. This integrates into the existing Dockerfile’s “build everything as root, then drop privileges” approach, making `brew` available at runtime without compiling it in the image. <h3>Confidence Score: 4/5</h3> - This PR is likely safe to merge, but the Homebrew ownership path should be corrected to avoid runtime failures when running as `node`. - The change is small and isolated to the Dockerfile, but the `chown` targets `/home/linuxbrew` rather than the actual copied prefix directory `/home/linuxbrew/.linuxbrew`, which can cause `brew` write operations to fail under the non-root user. - Dockerfile (Homebrew prefix ownership and paths) <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->