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

test/models/account/import_test.rb

@@ -226,6 +226,7 @@ class Account::ImportTest < ActiveSupport::TestCase
         name: account.name,
         board_count: Board.where(account: account).count,
         column_count: Column.where(account: account).count,
+        column_colors: Column.where(account: account).order(:id).pluck(:color),
         card_count: Card.where(account: account).count,
         comment_count: Comment.where(account: account).count,
         tag_count: Tag.where(account: account).count

test/models/column/colored_test.rb

@@ -7,6 +7,14 @@ class Column::ColoredTest < ActiveSupport::TestCase
     assert_equal Column::Colored::DEFAULT_COLOR, column.color
   end
 
+  test "reads color from legacy export format" do
+    column = columns(:writebook_triage)
+    # Broken exports serialized Color structs as JSON
+    column.update_column(:color, { "name" => "Lime", "value" => "var(--color-card-4)" }.to_json)
+
+    assert_equal Color.for_value("var(--color-card-4)"), column.reload.color
+  end
+
   test "update the column color" do
     columns(:writebook_triage).update!(color: "var(--color-card-3)")