feat: 31 - add skill test-data-management

[miroslavpojer]

Summary

Introduce a new skill for test data management, covering parametrized tests, factories, builders, and test isolation patterns.

Changes

• New skill definition: skills/test-data-management/SKILL.md
  • Covers parametrized tests, factory patterns, builder classes, test data cleanup, and determinism
  • Includes language-specific patterns (pytest, ScalaTest, xUnit, Jest, JUnit 5)
  • Examples for composable nested factories and avoiding test pollution

Files created

• skills/test-data-management/SKILL.md

Verification

• Frontmatter valid: name is kebab-case, matches directory, description covers "what" + "when to trigger" with explicit keywords, ≤ 1024 chars
• Body < 500 lines
• No hardcoded paths, credentials, or internal paths
• No script bundles requiring references

Closes #31