build: the exe is LlamaCasty.exe, and the publish script proves the artifact

Renames AssemblyName to LlamaCasty before the first Steam depot — Steamworks is explicit
that renaming a live exe is painful, so this had to land first, not later.

Four assembly-qualified pack URIs carried the old name, not three: MainWindow (window
icon), OverlayHost (logo), RenameRecordingDialog and KeepBroadcastDialog. Pack URIs
resolve by assembly name at runtime, so a stale one compiles, passes every test and then
silently renders nothing the first time that view opens. AssemblyIdentityTests guards
both halves — the assembly name, and no source XAML still naming the legacy assembly.
Packaging/Package.appxmanifest and package-msix.sh carry the exe name too.

scripts/publish.sh replaces the by-hand publish: single-file win-x64, ReadyToRun,
ffmpeg beside the exe, and it refuses to finish if ffmpeg, LICENSE, PRIVACY.md or
THIRD-PARTY-NOTICES.txt are missing, or if a test assembly leaked in.

That last guard exists because the first publish was wrong in a way no test could see:
PublishSingleFile + IncludeNativeLibrariesForSelfExtract bundled the libav*.dll family
into the exe — a 9-file output with no ffmpeg folder and a 182 MB binary, so the locator
would have found nothing at runtime. ExcludeFromSingleFile="true" on the content keeps
the folder a folder. Diffing against a control publish without the single-file flags
found it; guessing at item globs wasted two attempts first (recorded in MyMistakes.md).

Measured: 127 MB exe + 129 MB ffmpeg = 257 MB depot. Tests: AssemblyIdentity,
StorePackaging, BuildStamp, BundledFonts all pass; app builds with 0 warnings.

KeepBroadcastDialog.xaml

@@ -2,7 +2,7 @@
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         Title="Keep this broadcast?" Height="240" Width="460"
-        Icon="/ytLive;component/Assets/llamacasty-icon.png"
+        Icon="/LlamaCasty;component/Assets/llamacasty-icon.png"
         WindowStartupLocation="CenterOwner" ResizeMode="NoResize"
         ShowInTaskbar="False" Background="{StaticResource Brush.Background}">