Fix Jekyll Liquid syntax error in unification chapter

[Copilot]

Jekyll's Liquid engine was choking on {{X, two} in a C# code block, treating it as an unterminated variable expression and failing the build.

Change

Wrapped the offending code block in {% raw %} / {% endraw %} to prevent Liquid from processing C# dictionary initializer syntax:

+{% raw %}
 ```csharp
 var subst = new Dictionary<Hole, BinTerm>{{X, two}, {Y, stackOne}};

+{% endraw %}

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[Copilot]

Pull request overview

Fixes a Jekyll build failure caused by Liquid interpreting {{X, two} inside a C# code fence in the unification chapter.

Changes:

• Wrapped the affected C# fenced code block in {% raw %} / {% endraw %} so Liquid does not parse dictionary-initializer braces.

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