refine(skills): openfeature-eng - fix naming (2 segments, missing category)

## Summary

`openfeature-eng` has only 2 segments, missing the expected category structure.

## Current Name Analysis

- **Name**: openfeature-eng
- **Segments**: 2 (openfeature, eng)
- **Focus**: eng ✓ (valid)
- **Issue**: Missing category prefix

## Refinement Checklist

- [ ] Determine appropriate category for this skill
- [ ] Option A: Rename to `tool-openfeature-eng` (3 segments)
- [ ] Option B: Rename to `observability-openfeature-eng` (3 segments)
- [ ] Option C: Rename to `feature-flags-openfeature-eng` (4 segments)
- [ ] If renaming, update skill directory name
- [ ] If renaming, update SKILL.md frontmatter
- [ ] Run `just validate-skill components/skills/` to verify
- [ ] Update any references to this skill in other files

## Validation Command

```bash
just validate-skill components/skills/openfeature-eng
```