feat: deploy cmi agent skills via diffpy.app agentify

[ycexiao]

What problem does this PR address?

Closes #5

User can run

diffpy.app agentify  # cmi-skill folder will be created at ./.claude/skills/cmi-skill
diffpy.app agentify --agent codex  # cmi-skill folder will be created at ./.codex/skills/cmi-skill
diffpy.app agentify --system # cmi-skill folder will be created at $HOME/.claude/skills/cmi-skill
diffpy.app agentify --force  # cmi-skill folder will be updated

What should the reviewer(s) do?

Please check the modifications.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.11%. Comparing base (c9cb44b) to head (52a35d4).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #20      +/-   ##
==========================================
+ Coverage   92.94%   94.11%   +1.16%     
==========================================
  Files           4        5       +1     
  Lines         156      187      +31     
==========================================
+ Hits          145      176      +31     
  Misses         11       11              

Files with missing lines	Coverage Δ
tests/test_agentify.py	100.00% <100.00%> (ø)

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[ycexiao]

@sbillinge, it's ready for review.