feat(skills): unbind apps before force deletion

[squarezw]

Summary

• Add an unbind-all-and-delete action when a Skill is still bound to digital employees.
• Reuse the backend atomic force-delete path instead of issuing partial client-side unbind requests.
• Add loading and concurrent-binding handling, translations, and regression coverage.

Verification

• Targeted force-delete regression test passed.
• Production build passed.
• Git diff check passed.

Notes

• Biome reports pre-existing any warnings in hooks/useSkills.ts. This change removes the deletion-dialog any usage and adds no new warning.