Fix install script test timeout for macOS compatibility

[Copilot]

The install script CI workflow was failing on macOS runners because timeout command doesn't exist on macOS by default.

Changes

• Added cross-platform timeout detection in .github/workflows/install.yml
• Linux: uses native timeout command
• macOS: falls back to perl -e 'alarm shift; exec @ARGV' (Perl is available by default)

- timeout 10s ./install-gh-aw.sh v999.999.999 2>&1 | tee install-output.log || true
+ # Cross-platform timeout implementation
+ if command -v timeout > /dev/null 2>&1; then
+   timeout 10s ./install-gh-aw.sh v999.999.999 2>&1 | tee install-output.log || true
+ else
+   perl -e 'alarm shift; exec @ARGV' 10 ./install-gh-aw.sh v999.999.999 2>&1 | tee install-output.log || true
+ fi

The Perl-based approach avoids race conditions inherent to background process + kill patterns.

Original prompt

Review install script failure and fix the detection.

Reference: https://github.com/githubnext/gh-aw/actions/runs/19993149551/job/57336794162

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