Document backend/tools in repo-wide rules

Move the backend/tools note into the repo-wide rules section so it reads
as a standing convention rather than a backend command.

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

CLAUDE.md

@@ -64,6 +64,7 @@ These live in `.claude/skills/` and carry the detailed rules. Invoke the one tha
 **Keep comments short.** Comments should be concise, and focus on the "why" rather than the "what" (the code itself is the "what"). Avoid long paragraphs; break them into multiple lines or sentences.
 **Never commit secrets.** Never commit secrets (API keys, passwords, tokens, etc.) to the repo. Use environment variables or secret management tools instead.
 **Don't explain a change.** Avoid comments that explain why a change was made to the code. Focus instead on the current behaviour of the code and how it works.
+**Python tools live in `backend/tools/`.** Standalone dev/test utilities and scripts (not part of the app runtime) go in `backend/tools/`, not scattered across `backend/`.
 
 ---
 
@@ -81,8 +82,6 @@ uv run alembic revision --autogenerate -m "msg"   # new migration (then HAND-REV
 uv run alembic upgrade head         # apply migrations
 ```
 
-Standalone Python tools/scripts (dev/test utilities, not part of the app) live in `backend/tools/`.
-
 **Frontend** (`cd frontend`):
 
 ```bash