Review findings on the Task 1 commit (f6ff3b63):
1. Mapper.GetPreview is internal to ErsatzTV.Application, granted only to
ErsatzTV.Tests by convention (one-assembly-one-test-project). Move
ChannelPreviewTests.cs from ErsatzTV.Core.Tests to
ErsatzTV.Tests/Application/Channels, and revert the second
InternalsVisibleTo entry added to ErsatzTV.Application.csproj for
ErsatzTV.Core.Tests.
2. GetAllChannelsForApiHandlerTests.cs constructed `new
GetAllChannelsForApi()` at three sites, which no longer compiles now
that the record requires IptvJwtEnabled. Pass IptvJwtEnabled: false at
each site (all three tests are about plain channel listing/logo
mapping, not JWT).
ChannelController.GetAll's missing argument remains, deliberately, for a
later task.