chore(hygiene): keep the local CLAUDE.md out of the public tree

A project-level CLAUDE.md now points a fresh session at the working handoff
(`/_NEXT_SESSION.md`) and restates the invariants that must not be rolled back.
It is local navigation, not product documentation, so it stays untracked
alongside the handoff, the root audits and the planning notes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: JuliaEdom

.gitignore

@@ -117,6 +117,7 @@ reviews/*.err
 /_ref_*
 /[0-9][0-9]_[0-9][0-9]_[0-9][0-9].md
 /_NEXT_SESSION.md
+/CLAUDE.md
 /docs/NEXT_SESSION.md
 /docs/SESSION_HANDOFF.md
 /docs/data_flow.*