Drive the real GetChannelGuideHandler against a Testably fake filesystem
(seeded channels.xml + per-channel fragments) and a SQLite-backed
IDbContextFactory with one visible + one ShowInEpg=false channel, then
snapshot ChannelGuide.ToXml(). Covers the {RequestBase}/{AccessTokenUri}
substitution (the #1 regression surface), etv:-tag stripping, hidden-channel
exclusion, and assembly — with/without access token and with a base URL.
The volatile ?v={mtime} cache-buster is normalized. Same [CallerFilePath]
Goldens + ETV_UPDATE_GOLDENS harness as the M3U goldens (#11).
Core.Tests now references ErsatzTV.Application (handler lives there).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>