Fix setup-template.sh macOS compatibility with cross-platform sed approach

[Copilot]

Problem

The setup-template.sh script was failing on macOS with the error:

sed: 1: "README.md
": invalid command code

This occurred because macOS uses BSD sed, which requires an extension argument for the -i (in-place edit) flag, while Linux uses GNU sed where the extension argument is optional. The script was using sed -i "pattern" file, which works on Linux but fails on macOS.

Solution

Replaced all sed -i commands with a cross-platform replace_in_file() function that works on both BSD and GNU sed:

replace_in_file() {
    local file=$1
    local pattern=$2
    local replacement=$3
    sed "s|$pattern|$replacement|g" "$file" > "$file.tmp" && mv "$file.tmp" "$file"
}

This approach:

• Uses a temporary file instead of in-place editing
• Works identically on both macOS (BSD sed) and Linux (GNU sed)
• Maintains all original functionality without requiring OS detection

Changes

• Added replace_in_file() helper function
• Replaced 6 sed -i commands with calls to the new function
• No functional changes to the script behavior

Fixes the issue reported in the original issue where the setup script would fail on macOS systems.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Fix</issue_title>
<issue_description>@copilot the setup-template.sh fails on macOS with

sed: 1: "README.md
": invalid command code

I imagine this is a result of platform differences with sed. Use awk maybe.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #3

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