fix(docs): Use correct base path and versioned output for GitHub Pages

[ctreffs]

Description

This PR fixes the issue where the documentation deployment resulted in an empty page.

Changes

• Updated to support and variables for dynamic path configuration.
• Modified to:
  • Inject the correct (e.g., ) during the build.
  • Output documentation to a versioned subdirectory ().
  • Dynamically generate a root that redirects users to the version.
  • Added a post-deployment smoke test to verify the URLs.

Verification

• Local build verified with swift package --disable-sandbox
  --allow-writing-to-directory .build/documentation
  generate-documentation --target FirebladeMath
  --disable-indexing
  --transform-for-static-hosting
  --hosting-base-path math/main
  --output-path .build/documentation/main
  Extracting symbol information for 'FirebladeMath'...
  Finished extracting symbol information for 'FirebladeMath'. (0.55s)
  Building documentation for 'FirebladeMath'...

Finished building documentation for 'FirebladeMath' (0.82s)
Generated documentation archive at:
/Users/ctreffs/Developer/personal/game-dev/fireblade/fireblade-2026/Dependencies/Math/.build/documentation/main.

• CI includes a new smoke test job to confirm deployment success.

Fixes # (issue number if applicable)