fix: use extended regex in install.sh for macOS sed compatibility

[docer1990]

Summary

• Fix Java version detection failing on macOS despite Java 17+ being installed
• The sed command used \? (GNU basic regex extension) which is not supported by macOS BSD sed, causing the version parsing to silently fail
• Changed both sed calls to use -E (extended regex), which works on both macOS and Linux

Test plan

• Run bash install.sh on macOS — should show "Java 17 found"

[Copilot]

Pull request overview

This PR fixes Java version detection failing on macOS due to BSD sed incompatibility. The sed command used \? (a GNU basic regex extension) which silently fails on macOS BSD sed, causing version parsing to return empty results. The fix changes both sed calls to use -E (extended regex) with proper extended syntax, making the script portable across both macOS and Linux.

Changes:

• Converted two sed commands from basic regex with GNU extensions to POSIX-compliant extended regex using -E flag
• Changed \? (GNU extension) to ? and removed backslashes from parentheses to match extended regex syntax