Add bug-finding lint to the checks

Run ruff with pyflakes, syntax-error and bugbear rules only (no style
rules) over the integration, tests and scripts as part of check.sh and
CI. The codebase passes as is. Target Python 3.9 because the offline
tests are also run on older interpreters, which also leaves out the
zip(strict=) rule that needs 3.10. ruff 0.14.0 pinned in both test
requirement files.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/check.sh

@@ -4,6 +4,7 @@ set -eu
 # A transitive HA test dependency otherwise fetches metadata on import.
 export LITELLM_LOCAL_MODEL_COST_MAP=True
 python -m pip check
+python -m ruff check --no-cache .
 python -m unittest discover -s tests -v
 python -m pytest tests/ha -q
 python -m compileall -q custom_components/heating_mpc