Replace echo -e with printf in install-wp-tests.sh for POSIX compliance

[Copilot]

Addresses portability feedback on #356 regarding non-POSIX compliant echo -e usage in the generated install-wp-tests.sh template.

Changes

• Replaced all echo -e statements with printf for POSIX-compliant escape sequence handling
• Ensures the script works reliably across minimal sh implementations and various Unix-like systems

Example

Before:

echo -e "\033[0;32mSuccess message\033[0m"

After:

printf "\033[0;32mSuccess message\033[0m\n"

While the bash shebang (#!/usr/bin/env bash) makes echo -e functional, printf is the more portable and standard approach for formatted output with escape sequences.

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