Add tax treatment classification for investment accounts with international support (#693)

* Add tax treatment support for accounts, investments, and cryptos

* Replace hardcoded region labels with I18n translations

* Add I18n support for subtype labels with fallback to hardcoded values

* fixed schema

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Co-authored-by: luckyPipewrench <luckypipewrench@proton.me>

db/migrate/20260117200000_add_tax_treatment_to_cryptos.rb

@@ -0,0 +1,5 @@
+class AddTaxTreatmentToCryptos < ActiveRecord::Migration[7.2]
+  def change
+    add_column :cryptos, :tax_treatment, :string, default: "taxable", null: false
+  end
+end