fix: add legacy-html-assets generator

[flakey5]

Move asset folder copying to its own generator that we can call separately from the legacy-html generator

Description

Validation

Related Issues

Check List

• I have read the Contributing Guidelines and made commit messages that follow the guideline.
• I have run node --run test and all tests passed.
• I have check code formatting with node --run format & node --run lint.
• I've covered new added functionality with unit tests if necessary.

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Project	Deployment	Preview	Updated (UTC)
api-docs-tooling	Error		Nov 3, 2025 9:13pm

[codecov]

Codecov Report

❌ Patch coverage is 58.18182% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.62%. Comparing base (dca59d6) to head (78114a9).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/generators/legacy-html-assets/index.mjs	56.00%	22 Missing ⚠️
bin/commands/generate.mjs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #479      +/-   ##
==========================================
- Coverage   74.01%   72.62%   -1.39%     
==========================================
  Files         108      110       +2     
  Lines       10316    10553     +237     
  Branches      685      686       +1     
==========================================
+ Hits         7635     7664      +29     
- Misses       2678     2886     +208     
  Partials        3        3              

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[avivkeller]

I don't love this approach, it feels like a waste of a generator. This should, IMO, be one generator, or no generators and handled by the Makefile (although I'd prefer the former)