Fix markdown syntax highlighting by mapping capture names

The markdown tree-sitter grammar uses nvim-treesitter capture names
(e.g. text.title, punctuation.special) that CaptureName.fromString()
didn't recognize, causing all markdown highlights to be silently dropped.

Map these to existing CaptureName cases so no new enum values or theme
changes are needed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Sources/CodeEditSourceEditor/Enums/CaptureName.swift

@@ -92,6 +92,18 @@ public enum CaptureName: Int8, CaseIterable, Sendable {
             return .keywordReturn
         case "keyword.function":
             return .keywordFunction
+        case "text.title", "text.strong", "punctuation.special":
+            return .keyword
+        case "text.literal", "text.uri", "string.escape":
+            return .string
+        case "text.reference":
+            return .type
+        case "text.emphasis":
+            return .variable
+        case "punctuation.delimiter":
+            return .comment
+        case "none":
+            return nil
         default:
             return nil
         }