[FEATURE] Delete skill folders for removed packages

[rcollette]

Is your feature request related to a problem? Please describe.
When a package is removed, skill folders are not being deleted.

[richard.collette:~/] 012-java-service-bootstrap(+1650/-1247,2) 2 ± apm install --target copilot
[>] Installing dependencies from apm.yml...
[!] Could not fetch org policy from org:gitlab.com/myorg/.github (HTTP 410 fetching policy from gitlab.com/myorg/.github); proceeding without policy enforcement. Retry, check connectivity, or use --no-policy to bypass.
[i] Targets: copilot  (source: --target flag)
  [+] github.com/MyOrg/apm-internal-marketplace/packages/coding-standards-core @a995c83c (cached)
  |-- 1 prompts integrated -> .github/prompts/
  |-- 3 agents integrated -> .github/agents/
  |-- 3 instruction(s) integrated -> .github/instructions/
  [!] [MyOrg/apm-internal-marketplace/packages/coding-standards-python-fastapi] Refused to remove directory entry .agents/skills/coding-standards-python-fastapi: APM only deletes individual files. If this entry was added by a malicious or corrupt lockfile, remove it manually from apm.lock.yaml.
  [!] [MyOrg/apm-internal-marketplace/packages/coding-standards-python] Refused to remove directory entry .agents/skills/coding-standards-python: APM only deletes individual files. If this entry was added by a malicious or corrupt lockfile, remove it manually from apm.lock.yaml.
  [!] 1 dependency unpinned: MyOrg/apm-internal-marketplace -- add #tag or #sha to prevent drift
[*] Installed 1 APM dependency in 0.3s.

Describe the solution you'd like
Package artifacts should be removed