docs(README): lineage without a pointer to a repository being deleted

[y1o1]

Summary

The lineage note named dplaasio/auth at c23ff3f as this repository's origin.
That org is being deleted, so on a repository whose whole subject is verifiable
provenance, the first provenance claim a reader meets would have pointed at
nothing checkable — and it was never checkable publicly anyway, the predecessor
having always been private.

The rewrite keeps the fact a reader actually needs (why the history starts where
it does) and drops the identifier they cannot resolve.

-> **Lineage**: forked from `dplaasio/auth` (the dPLaaS PoC auth stack) at `c23ff3f`,
-> then renamed to the dplaax protocol namespace …
+> **Lineage**: this repository's history starts at the public cut, not at the
+> start of the work. … That predecessor was retired rather than published, so
+> there is no upstream repository to link to; the earliest commit here is the
+> snapshot the public line begins from.

git grep dplaasio and git grep c23ff3f are now both empty across the repo.

Test plan

Documentation only. No code, no workflow, no generated template touched.

🤖 Generated with Claude Code