Log custom rule compilation failures as error

When a custom rule fails to compile, the failure log at a debug level and one must run `npx whine --debug` to surface the error, which can be confusing. It would be less confusing if compilation errors on custom rules were logged at an error level.

Start by running a custom rule that fails to compile, then compare the output of `npx whine` with `npx whine --debug`. Trace where custom-rule compilation failures are logged. Done means the failure appears at error level without requiring the debug flag, while the existing command still reports the compilation failure.

Written by the indexing model from the issue text.