Fix clear fallback for unknown Ghostty terminfo

[mcclayton]

Summary

• wrap the managed clear command so interactive shells use the existing ANSI fallback when terminfo does not know xterm-ghostty
• make clearTerminal call the real binary via command clear to avoid recursion through the wrapper
• extend terminal compatibility coverage to assert typed clear is available and quiet

Validation

• bash -n config/dotfiles/mac/bashrc.sh ci/test_terminal_compat.sh
• bash ./ci/test_terminal_compat.sh
• bash ./ci/checks.sh
• git diff --check