Stop tracking robochatto.env and robochatto.db
These local bot state files never belonged in the library repo.
robochatto.env in particular carried credentials, so anything that was
ever committed to it must be treated as leaked.
Also add .mypy_cache/ and .ruff_cache/ to .gitignore to prevent future
accidental commits from tooling caches.
Note: this only stops future tracking. The files remain in git history
(commits 1589fe6 and 56d7089 among others); scrubbing history would
require a force-push rewrite of main. Credential rotation is tracked
in bean chattolib-si6t.
TheCodemancer