Add vuln-report-writing skill for professional penetration testing and bug bounty hunting

[CristiVlad25]

This skill is useful for cybersecurity professionals as it helps with report writing in 2 ways:

1. Writes reports for individual findings (vulnerabilities/bugs) that can be used on bug bounty platforms.
2. Writes penetration testing reports, based on all the findings.

In short:

• Adds new skill skills/.experimental/vuln-report-writing
• Provides a strict, triage-friendly format for bug bounty findings and pentest reports
• Includes templates and OWASP reference list to keep reports consistent and reproducible

Contents

• skills/.experimental/vuln-report-writing/SKILL.md
• skills/.experimental/vuln-report-writing/references/bugbounty-finding.md
• skills/.experimental/vuln-report-writing/references/pentest-report.md
• skills/.experimental/vuln-report-writing/references/owasp-refs.md
• skills/.experimental/vuln-report-writing/LICENSE.txt

Testing

• Not applicable (documentation/skill content only)