1.4-P3: SkillCollection child SkillCard creation for git-sourced entries

## SkillCollection Child SkillCard Creation (Phase 3)

Part of Stream 1: Controller (#5) | Parent: #1 | Related: #12

Deferred from 1.4 (SkillCollection controller). Phase 3 work.

### Tasks

- [ ] Create child SkillCard CRs for git-sourced entries in the collection
- [ ] Set ownership references so child SkillCards are garbage collected
- [ ] Unit tests: child creation, lifecycle management

### Acceptance Criteria

- SkillCollection with git-sourced entries creates child SkillCard CRs
- Child SkillCards have owner references pointing to the parent SkillCollection
- Deleting the SkillCollection garbage collects child SkillCards