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.Tests/LocalizationTests.cs

@@ -128,9 +128,9 @@ public sealed class LocalizationTests : IDisposable
     {
         Localizer.Instance.SetLanguage(AppLanguage.Russian);
 
-        Localizer.Instance.Plural("Parse.Count.Records", 1).ShouldBe("1 запись");
-        Localizer.Instance.Plural("Parse.Count.Records", 3).ShouldBe("3 записи");
-        Localizer.Instance.Plural("Parse.Count.Records", 7).ShouldBe("7 записей");
+        Localizer.Instance.Plural("Collect.Count.Images", 1).ShouldBe("1 изображение");
+        Localizer.Instance.Plural("Collect.Count.Images", 3).ShouldBe("3 изображения");
+        Localizer.Instance.Plural("Collect.Count.Images", 7).ShouldBe("7 изображений");
     }
 
     [Fact]
@@ -195,7 +195,7 @@ public sealed class LocalizationTests : IDisposable
 
     [Fact]
     public void A_fallback_is_used_when_a_key_is_absent() =>
-        Localizer.Instance.GetOrDefault("Parser.brand-new.Name", "Brand new").ShouldBe("Brand new");
+        Localizer.Instance.GetOrDefault("Source.brand-new.Name", "Brand new").ShouldBe("Brand new");
 
     [Theory]
     [InlineData(AppLanguage.English, "en")]