[manuelmayer-dev]

Closes #935

Summary

A failing background service no longer stops the host: the backup scheduler logs the error and retries, and startup services that gate readiness still stop the host explicitly. DatabaseContext opens unpooled connections until Microsoft.Data.Sqlite ships the fix for dotnet/efcore#39008.

Testing

Full solution Release build with warnings as errors and all test suites pass, apart from the Plugin.Cli build test that also fails locally on main. New tests cover the scheduler retry, readiness failures and a throwing background service. Checked in a disposable host with an injected SQLite failure: before, the host stopped; after, it logged the error and the retry created the scheduled backup. The disposed pooled handle itself could not be reproduced on demand.

Checklist

• Tests were added or updated where needed
• The change was verified manually where appropriate
• Documentation was updated if the change affects documented behaviour
• I reviewed and understand every submitted change