XML validation error when using the -x flag due to unescaped special characters

[imertz]

Problem

When using the -x flag to export a Git repository as XML, the tool fails with the following error:

Error: XML validation error on line 494: invalid character entity & (no semicolon)

Steps to Reproduce

1. Clone any repository containing files with special XML characters (like '&')
2. Run the following command:

   git2gpt -x -s -e -o output.xml /path/to/repository

3. Observe the XML validation error

Cause

The issue is in the OutputGitRepoXML function in prompt/prompt.go. The current implementation doesn't properly escape special characters in XML content or handle CDATA sections correctly.

Special XML characters (&, <, >, ", ') need proper escaping when outside CDATA sections, and the CDATA terminator sequence ]]> needs special handling when it appears within file contents.