fix(skill-package): index admitted path descendants

[Yevanchen]

Summary

• Replaced skill-package path descendant collision scans with an indexed admission state.
• Added regression coverage for rejecting file/child collisions regardless of insertion order.

Why

• Skill package normalization is used for archive import/export paths; checking every admitted path for descendants made collision admission O(n^2) as package entry counts grew.

Verification

• Commands:
  • just test-package @mosoo/skill-package
  • just tc-package @mosoo/skill-package
  • just fmt-check-path pkgs/skill-package/src/path-admission.ts
  • just fmt-check-path pkgs/skill-package/tests/path-admission.test.ts
  • bun run --filter @mosoo/skill-package lint
  • TMPDIR=/private/tmp just check
  • just commit-check
• Manual steps:
  • Ran complexity-optimizer scanner against the repo and inspected the reported owned-code hotspots.
• Not run:
  • N/A

Impact

• User/API/contract changes:
  • None.
• Generated files / GraphQL / DB / lockfile:
  • None.
• Env or config changes:
  • None.
• Risk and rollback:
  • Low. Change is localized to path admission bookkeeping and preserves existing error behavior. Roll back the single commit if archive path admission regresses.

Review

• Closest review areas:
  • pkgs/skill-package/src/path-admission.ts
  • pkgs/skill-package/tests/path-admission.test.ts
• Known trade-offs:
  • The scanner still flags ordinary path-depth iteration in this package; the O(number of admitted entries) descendant scan has been removed.