feat: rewrite redirects sent through the proxy

[mattmess1221]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation, readme or JSDoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Rewrite redirects if for some reason an API uses them.

• Absolute and same-origin locations will be rewritten.
  • Locations to outside the endpoint's URL path are unsupported and will cause a Server Error.
• Relative and cross-origin locations will not be rewritten.

Also moves the config template typing to a static .d.ts file with module declarations, as it was the best way to add typing for server templates.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[Copilot]

Pull request overview

This PR adds support for rewriting redirect responses when proxying API requests, ensuring redirects are properly handled in both SSR and client-side contexts. The feature is controlled by a new experimental configuration option rewriteProxyRedirects (enabled by default).

Key changes:

• Implements redirect rewriting logic for proxied requests, handling relative, absolute, and same-origin redirects
• Adds configuration option to enable/disable the feature
• Includes test coverage for various redirect scenarios

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/runtime/server/proxyHandler.ts	Core implementation of redirect rewriting logic with helper functions
src/module.ts	Adds configuration option and server template for the feature
test/fixture/server/api/redirect.get.ts	Test fixture for various redirect scenarios
test/e2e-proxy.test.ts	E2E tests validating redirect rewriting behavior
src/runtime/server/handler.ts	Adds header to track redirected responses
playground/server/api/custom/redirect.ts	Playground endpoint for testing redirects
playground/server/api/custom/echo.ts	Playground endpoint for testing requests
playground/nuxt.config.ts	Adds custom endpoint to playground configuration

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[mattmess1221]

Turns out addTemplate forces write = true when the filename ends in .d.ts lol