Refactor node show argument to use Enum for better validation and clarity

[Xyc2016]

Refactor node show argument to use a typed Enum instead of a raw string.

• Replace manual string validation with ShowTarget(StrEnum)
• Improve CLI validation and error message clarity

[codecov]

Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
comfy_cli/command/custom_nodes/command.py	81.81%	2 Missing ⚠️

@@            Coverage Diff             @@
##             main     #346      +/-   ##
==========================================
+ Coverage   52.11%   52.35%   +0.24%     
==========================================
  Files          32       32              
  Lines        3527     3528       +1     
==========================================
+ Hits         1838     1847       +9     
+ Misses       1689     1681       -8     

Files with missing lines	Coverage Δ
comfy_cli/command/custom_nodes/command.py	43.34% <81.81%> (+2.24%)	⬆️

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[Xyc2016]

The failing CI checks are not caused by this PR.
They fail during ComfyUI dependency resolution on Python 3.9 (comfy-kitchen requires >=3.10).

[bigcat88]

@Xyc2016 can you please rebase this PR on main? I had removed python3.9 from the CI.

[bigcat88]

Thanks for this refactoring! Merging