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>

src/AvParser.UI/ViewModels/CollectErrorViewModel.cs

@@ -0,0 +1,40 @@
+using AvParser.Core.Parsing;
+using AvParser.UI.Localization;
+using ReactiveUI;
+
+namespace AvParser.UI.ViewModels;
+
+/// <summary>One row of the collect error list, with its message translated.</summary>
+/// <remarks>
+/// Sources and the fetcher are part of the domain and produce English text plus a code. This resolves
+/// <c>Collect.Error.{Code}</c> and falls back to the domain's own wording, so a code that has not
+/// been translated yet still says something useful instead of showing a missing-key marker.
+/// </remarks>
+public sealed class CollectErrorViewModel(ParseError error) : ReactiveObject
+{
+    /// <summary>The underlying error.</summary>
+    public ParseError Error { get; } = error ?? throw new ArgumentNullException(nameof(error));
+
+    /// <summary>1-based position of the offending item: a pasted line, or a place in a listing.</summary>
+    public int Index => Error.Index;
+
+    /// <summary>Translated message.</summary>
+    public string Text
+    {
+        get
+        {
+            if (Error.Code is not { Length: > 0 } code)
+            {
+                return Error.Message;
+            }
+
+            var template = Localizer.Instance.GetOrDefault($"Collect.Error.{code}", Error.Message);
+            return Error.Arguments.Count == 0
+                ? template
+                : string.Format(Localizer.Instance.Culture, template, [.. Error.Arguments]);
+        }
+    }
+
+    /// <summary>Re-reads the translated message.</summary>
+    public void Refresh() => this.RaisePropertyChanged(nameof(Text));
+}