Read an unknown textCapitalization as none

The Meridian branch's enum read unknown values as none; master's field
only had a default, so a stray value failed the whole text field.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019VxYXXsxhYd3bYhrw4WpZy

Author: claude

lib/src/api/nodes/text_field_node.dart

@@ -216,7 +216,10 @@ class TextFieldProperties extends CustomProperties with FieldsHolder {
 
   /// Which letters the on-screen keyboard capitalizes by default: none,
   /// the first of each word (names), of each sentence, or every letter.
-  @JsonKey(defaultValue: TextCapitalizationC.none)
+  @JsonKey(
+    defaultValue: TextCapitalizationC.none,
+    unknownEnumValue: TextCapitalizationC.none,
+  )
   TextCapitalizationC textCapitalization;
 
   /// A ring drawn around the field while it has focus, [focusRingWidth]