chore: housekeeping — linter & formatter setup

Add .prettierrc.json, .markdownlint.json, .yamllint.yaml, .gitattributes
Run CSharpier, Prettier and markdownlint across the entire codebase.
No logic changes — formatting, using order and line endings only.

HellionChat/Ui/TabTintCache.cs

@@ -23,9 +23,11 @@ internal static class TabTintCache
     {
         var name = tab.TellTarget.Name;
         var world = tab.TellTarget.World;
-        if (tab._cachedTellIcon is null
+        if (
+            tab._cachedTellIcon is null
             || tab._cachedIconTellName != name
-            || tab._cachedIconTellWorld != world)
+            || tab._cachedIconTellWorld != world
+        )
         {
             tab._cachedIconTellName = name;
             tab._cachedIconTellWorld = world;