Docs for v1.0.0-alpha3

Point-in-time snapshot of the kagent documentation at the kagent v1.0.0-alpha3 release.

Publishing this release runs Update Reference Documentation against the kagent
v1.0.0-alpha3 tag and opens a pull request regenerating the 0.x API, Helm, and CLI
references along with the 1.x version conrefs.

First docs release cut for the 1.x version line in this repository, so there is no earlier tag to
generate a changelog from. Later releases carry the usual What's Changed list.