Fix export/import losing custom column colors

record.to_json serializes through model accessors. Column::Colored
overrides the color accessor to return a Color struct, which serializes
as {"name":"Blue","value":"var(--color-card-default)"} instead of the
raw CSS string.

Two fixes:
- Export raw DB values via record.attributes.slice(*attributes).to_json
- Color.for_value parses legacy JSON format so columns imported from
  old exports self-heal when read

app/models/account/data_transfer/record_set.rb

@@ -65,7 +65,7 @@ class Account::DataTransfer::RecordSet
     end
 
     def export_record(record)
-      zip.add_file "data/#{model_dir}/#{record.id}.json", record.to_json
+      zip.add_file "data/#{model_dir}/#{record.id}.json", record.attributes.slice(*attributes).to_json
     end
 
     def files

app/models/color.rb

@@ -2,9 +2,23 @@ Color = Struct.new(:name, :value)
 
 class Color
   class << self
+    # Finds a Color by its CSS value (e.g. "var(--color-card-4)").
+    # Falls back to extracting the value from legacy export formats where
+    # the Color struct was serialized instead of the raw CSS string.
     def for_value(value)
-      COLORS.find { |it| it.value == value }
+      COLORS.find { |it| it.value == value } ||
+        extract_from_legacy_export(value)
     end
+
+    private
+      # Broken exports serialized Color structs instead of raw CSS values,
+      # producing JSON like {"name":"Lime","value":"var(--color-card-4)"}.
+      # Parse it and extract the value.
+      def extract_from_legacy_export(value)
+        parsed = value.is_a?(String) && JSON.parse(value)
+        COLORS.find { |it| it.value == parsed["value"] } if parsed.is_a?(Hash)
+      rescue JSON::ParserError
+      end
   end
 
   def to_s