fix(build): safely append Homebrew paths to avoid overriding user toolchains

[solderzzc]

Refines the previous PATH injection in build.sh based on PR review. Instead of globally prepending the Homebrew binary directories, they are now safely appended to the PATH only if they exist and are not already present. This ensures that any custom user toolchains (like explicit cmake or swift paths) take priority while safely falling back to native Homebrew paths on Apple Silicon.

[Copilot]

Pull request overview

Updates build.sh PATH handling so Homebrew tool directories are appended only when present and not already included, avoiding unintentional precedence over user-provided toolchains.

Changes:

• Replace unconditional Homebrew PATH prepending with conditional PATH appends for /opt/homebrew/bin.
• Add conditional PATH append for /usr/local/bin to support Intel Homebrew layouts while preserving existing PATH precedence.

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[Copilot]

Appending with export PATH="$PATH:/opt/homebrew/bin" (and similarly for /usr/local/bin) will introduce an empty PATH element if $PATH is empty/unset, which makes the current working directory searchable (PATH=":/opt/homebrew/bin"). Consider using a safe append pattern (e.g., only add the : when $PATH is non-empty) to avoid this security/behavior risk.

Suggested change

	export PATH="$PATH:/opt/homebrew/bin"
	fi
	if [[ ":$PATH:" != *":/usr/local/bin:"* ]] && [ -d "/usr/local/bin" ]; then
	export PATH="$PATH:/usr/local/bin"
	export PATH="${PATH:+$PATH:}/opt/homebrew/bin"
	fi
	if [[ ":$PATH:" != *":/usr/local/bin:"* ]] && [ -d "/usr/local/bin" ]; then
	export PATH="${PATH:+$PATH:}/usr/local/bin"