feat: add weak password detection skill (#621)

[Stark-SK]

Summary

Adds a new skill weak_password_detection covering weak password detection, credential stuffing, brute-force testing, and Hydra-based authentication attacks.

What It Covers

• Weak password policy detection and common password testing
• Default/hardcoded credential identification
• Credential stuffing with breach database approaches
• System-generated password prediction
• Brute-force tooling: Hydra, ffuf, Patator, custom scripts
• Service-level attacks (SSH, FTP, RDP, SMB, databases)
• API and mobile-specific brute-force techniques
• Validation methods and false positive avoidance

Why This Matters

Issue #621 requested weak password detection functionality. This skill enables Strix agents to systematically test for weak credentials across web apps, APIs, and services using industry-standard tools and methodologies.

Testing

• Skill follows the established strix/skills/ format with YAML frontmatter
• Content includes practical examples, validation methods, and false positive guidance
• Pre-commit hooks pass

Closes #621

[greptile-apps]

Greptile Summary

This PR adds a new weak password detection skill. The main changes are:

• New weak_password_detection vulnerability skill.
• Coverage for password policy checks, default credentials, credential stuffing, and brute-force workflows.
• Examples for Hydra, ffuf, Patator, custom scripts, validation, and false positives.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
strix/skills/vulnerabilities/weak_password_detection.md	Adds a new skill document for weak password detection using the existing skill frontmatter and markdown format.

_{Reviews (1): Last reviewed commit: "feat: add weak password detection skill ..." | Re-trigger Greptile}