Remove the demo text-parsing domain

The scaffolding domain existed to prove the shell end to end before there was
anything real to put in it. There is now, so it goes - as CLAUDE.md promised it
would.

Gone: the two sample parsers, ITextParser, ParsedRecord, the parser catalog,
ParseViewModel and ParseView, their tests, and the settings key that remembered
which parser was last used. ParseError.LineNumber becomes Index, since for a
listing "line 42" was simply untrue, and the error keys move from Parse.Error.*
to Collect.Error.* now that parsing is not a concept here.

Kept: IParser<,>, ParseOutcome, ParseProgress and ParseError. The streaming
contract was always the general part - it was only ever the text-shaped closure
of it that was scaffolding.

Rendering the dashboard caught two keys that were referenced but never added
during the rename: the XAML was repointed and the resources were not. The parity
test could not see it, because it compares the two files against each other and
a key absent from both is consistent. That gap now has its own test, which reads
every {l:Loc} in the XAML and checks it resolves - a screenshot is too late and
too manual a way to find a missing string.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/AvParser.UI.HeadlessTests/LocalizationViewTests.cs

@@ -19,7 +19,7 @@ public sealed class LocalizationViewTests : IDisposable
 
     private static (ShellView View, ShellViewModel ViewModel) ShowShell()
     {
-        var navigation = new NavigationService([new FakePage("Page.Dashboard"), new FakePage("Page.Parse")]);
+        var navigation = new NavigationService([new FakePage("Page.Dashboard"), new FakePage("Page.Collect")]);
         var viewModel = new ShellViewModel(navigation, new FakeThemeService(), ImmediateSequencer.Instance);
         var view = new ShellView { DataContext = viewModel };
 
@@ -49,14 +49,14 @@ public sealed class LocalizationViewTests : IDisposable
         var (view, _) = ShowShell();
 
         var english = RailLabels(view);
-        english.ShouldBe(["Dashboard", "Parse"]);
+        english.ShouldBe(["Dashboard", "Collect"]);
 
         Localizer.Instance.SetLanguage(AppLanguage.Russian);
         Dispatcher.UIThread.RunJobs();
 
         // The same controls, not a rebuilt tree: this is the whole point of binding through the
         // localizer's indexer rather than resolving strings once at load.
-        RailLabels(view).ShouldBe(["Обзор", "Разбор"]);
+        RailLabels(view).ShouldBe(["Обзор", "Сбор"]);
     }
 
     [AvaloniaFact]