feat(ssg): add redirect plugin

[3w36zj6]

close #4389

The author should do the following, if applicable

• Add tests
• Run tests
• bun run format:fix && bun run lint:fix to format the code
• Add TSDoc/JSDoc to document the code

[codecov]

Codecov Report

❌ Patch coverage is 89.28571% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.56%. Comparing base (bde9a03) to head (4c565a9).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/helper/ssg/plugins.ts	88.88%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4599      +/-   ##
==========================================
- Coverage   91.56%   91.56%   -0.01%     
==========================================
  Files         173      174       +1     
  Lines       11256    11284      +28     
  Branches     3265     3272       +7     
==========================================
+ Hits        10307    10332      +25     
- Misses        948      951       +3     
  Partials        1        1              

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[3w36zj6]

The specification mandates that redirect responses must include a Location header ¹. Current implementations simply bypass generating the file if no Location header is present, though options include displaying a warning or throwing an error could be considered.

Footnotes

1. https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Location ↩

[3w36zj6]

Since built-in plugins should only handle lightweight ones, I decided to manage multiple plugins in a single plugins.ts file. This should make updating exports slightly more convenient.