Align Release Tag and `RERUM_API_VERSION`

The hard coded 1.0.0 tag is still used throughout. We can use that for internal stamping, but we should consider how the release tags and API version align. There is a `RERUM_API_VERSION` env, a `__rerum.APIVersion` property, and noted API version on API.html to consider.

Start by locating the hard-coded 1.0.0 references, the RERUM_API_VERSION environment variable, the __rerum.APIVersion property, and the API version noted on API.html. Compare these sources with the repository's release tags and define a consistent relationship between them. Done means the alignment is decided and reflected across all identified version sources.

Written by the indexing model from the issue text.