fix: EF Core logs from Warning up, not every SQL command

[ThorSPB]

Closes #43

What

• appsettings.json: Microsoft.EntityFrameworkCore at Warning. This applies to the API and to the timetable import, which reads the same file; the import's own Warning minimum was being overridden by Default: Information.
• README: the config row says how to see SQL again while debugging.
• Test: SQL commands are off at Information, EF warnings stay on, the app's own Information stays on.

Testing

• CI. Without the setting, Default: Information applies and the first assertion fails.
• After deploy: stage's api.log gets no new Executed DbCommand entries, and an import dry run prints only the summary and warnings.

🤖 Generated with Claude Code