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Follow-up to Homebrew discussion: https://github.com/orgs/Homebrew/discussions/6617.

This PR updates the newly added FAQ section "What is the default ownership and permissions used by Homebrew" (introduced in #20946) to avoid two misleading statements:

• Clarifies that Homebrew-installed binaries run with the invoking user's privileges. Removes and adjusts wording implying binaries "inherit" admin permissions or can read/modify system locations by default.
• Fixes wording that discourages a dedicated Homebrew user account, aligning it with existing FAQ guidance that recommends a dedicated account for multi-user environments (see "Why does Homebrew say sudo is bad?": https://docs.brew.sh/FAQ#why-does-homebrew-say-sudo-is-bad).