docs: update architecture and SDK reference for bug fixes

[Theauxm]

Summary

• Updated DataContext section in effect architecture docs: Track/Update use direct entity state assignment instead of EF Core's graph-traversing Update(). Navigation properties are not cascaded across DI scope boundaries.
• Updated EffectRunner section: all three operations (Track, Update, SaveChanges) await providers sequentially.
• Updated TraxLambdaFunction error handling docs: errors are now logged before returning RemoteJobResponse. Clarified pre-train vs in-train error persistence.
• Updated AddTraxJobRunner error path: notes that errors are logged.

Companion to TraxSharp/Trax.Effect#46 and TraxSharp/Trax.Scheduler#40.

Test plan

• Verify docs render correctly (markdown only, no code changes)