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.Infrastructure.Tests/JsonSettingsServiceTests.cs

@@ -56,7 +56,6 @@ public sealed class JsonSettingsServiceTests : IDisposable
             """
             {
               "theme": "System",
-              "lastParserId": "delimited",
               "windowWidth": 1280,
               "windowHeight": 800,
               "windowMaximized": false,
@@ -76,7 +75,6 @@ public sealed class JsonSettingsServiceTests : IDisposable
         settings.Language.ShouldBe(AppLanguage.System);
 
         // And the values the file did carry must survive.
-        settings.LastParserId.ShouldBe("delimited");
         settings.MinimumLogLevel.ShouldBe("Information");
     }