docs: rename CLAUDE.md to AGENTS.md and rebrand provider-agnostic

Delete CLAUDE.md in favor of AGENTS.md as the orientation doc, rebrand
the project from Codex-bottle to provider-agnostic bot-bottle, and
repoint every CLAUDE.md reference across PRDs, research notes, the
implementer agent example, and the yaml_subset comment.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/prds/0023-smolmachines-backend.md

@@ -201,7 +201,7 @@ The feature is **done** when all of the following ship:
   smolmachines-capable host. The suite is updated to skip cleanly
   on hosts that can't reach smolmachines (same shape as the
   existing `GITEA_ACTIONS == "true"` skip), not to fail.
-- README + `CLAUDE.md` updated to document the env-var selection,
+- README + `AGENTS.md` updated to document the env-var selection,
   the macOS-only scope for v1, and the `smolvm` install
   prerequisite.