Fix have_attribute_row selector for labels containing slashes

[Copilot]

ActiveAdmin normalizes / to _ when generating row CSS classes (e.g. "USA/UAH" → row-usa_uah), but attributes_row_selector only replaced spaces, producing an invalid selector tr.row.row-usa/uah > td.

Changes

• selectors/attributes_table.rb: Replace both whitespace and / with _ using /[\s\/]/ regex, matching ActiveAdmin's class generation
• spec/lib/selectors/attributes_table_spec.rb: Add unit tests for attributes_row_selector covering the slash and mixed slash/space cases

# Before
label = label.to_s.gsub(' ', '_').downcase
# "USA/UAH" → "tr.row.row-usa/uah > td"  ❌

# After
label = label.to_s.gsub(/[\s\/]/, '_').downcase
# "USA/UAH" → "tr.row.row-usa_uah > td"  ✓