docs: remove the second contributing note and its dead pointers

CONTRIBUTING-AI.md pointed contributors at a CLAUDE.md "checked in and
kept current"; that file is not in the repository, so the pointer and
the twenty references to it in folder READMEs, docs and comments led
nowhere. The note goes; its one lasting rule (whoever commits a change
stands behind it, no real names, no live health figures, no secrets)
moves into CONTRIBUTING.md. The folder READMEs keep their own content
and drop the dead link, and a reference to the unpublished planning
folder goes with it.

The checked-in .mcp.json was a local editor config no workflow reads;
it is untracked and ignored now. The translation tiers are described
as machine-translated first drafts reviewed by the community, and the
list names Russian, which it missed.

scripts/README.md

@@ -42,4 +42,4 @@ typecheck.
 
 ## Conventions
 
-See [`../CLAUDE.md`](../CLAUDE.md) "Tests and commands" + "Self-hosting gotchas". Operator runbooks that drive these scripts live in [`../docs/ops/`](../docs/ops/).
+Operator runbooks that drive these scripts live in [`../docs/ops/`](../docs/ops/).