Python script only packages FE support

[cdcme]

Related issue: Resolves #48394

Adds .py to the custom-package upload form and software details page, accepted and detected as a script-only package (advanced options follow .sh/.ps1), shown with the Python icon and per-platform file-type tooltips, and mapped to the py_packages source that renders as "Script-only package (macOS & Linux)".

Checklist for submitter

• Added/updated automated tests
• QA'd all new/changed functionality manually

Manual QA

• Verified live in the browser against a dev server

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.11%. Comparing base (646ebd0) to head (c3fb7dd).

Files with missing lines	Patch %	Lines
...ePage/components/forms/PackageForm/PackageForm.tsx	33.33%	2 Missing ⚠️
frontend/utilities/software_install_scripts.ts	0.00%	1 Missing ⚠️
frontend/utilities/software_uninstall_scripts.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                        Coverage Diff                        @@
##           feat/41470-python-script-only   #48946      +/-   ##
=================================================================
- Coverage                          68.11%   68.11%   -0.01%     
=================================================================
  Files                               3709     3709              
  Lines                             235099   235105       +6     
  Branches                           12352    12355       +3     
=================================================================
+ Hits                              160129   160133       +4     
- Misses                             60593    60595       +2     
  Partials                           14377    14377              

Flag	Coverage Δ
frontend	59.28% <60.00%> (+<0.01%)	⬆️

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[cdcme]

@claude review once