CVE-2026-49987: repomix Vulnerable to Command Injection (RCE) via `--remote-branch` Argument Injection

The --remote-branch CLI option in repomix is vulnerable to argument injection. User-supplied input is passed directly to git fetch and git checkout subprocesses via child_process.execFileAsync without sanitization, -- delimiters, or validation.

An attacker can inject arbitrary git command-line options. By injecting the --upload-pack option and specifying an SSH (git@...) or local (file://) remote URL, an attacker achieves arbitrary command execution with the privileges of the user running repomix. This bypasses the existing dangerousParams blocklist implemented in validateGitUrl().