Function parse_shell_file 

pub fn parse_shell_file(
    path: &Path,
    target_var: &str,
    current_value: Option<&str>,
) -> Result<Vec<ParsedShellEntry>>

Parse a shell script file for variable assignments

Handles common bash/zsh patterns:

• export VAR=value
• VAR=value
• export VAR (export existing variable)
• unset VAR
• PATH=“$PATH:new” (append)
• PATH=“new:$PATH” (prepend)
• [ -f x ] && export VAR=y (conditional)
• source file / . file