Fix Broken Account Re-linking Feature (#469)

* Update SimpleFIN relinking flow and enhance duplicate account handling

- Updated logic to allow relinking of SimpleFIN accounts while preserving legacy mappings.
- Introduced clean-up logic to hide orphaned duplicate accounts after relinking.
- Enhanced UI to display current mappings for linked accounts.
- Improved test coverage for relinking scenarios and SimpleFIN account visibility.

* Localize SimpleFIN account selection messages and remove hardcoded text

- Added translations for user-facing messages in `select_existing_account` flow (`pt-BR` and `en` locales).
- Replaced hardcoded strings in the view with localized keys.

* Localize Enable Banking and SimpleFIN account linking messages; add support for investment accounts.

- Added translations for Enable Banking and SimpleFIN account linking flows.
- Updated views and controllers to replace hardcoded strings with localized keys.
- Introduced support for investment accounts in `Provider::LunchflowAdapter`.
- Enhanced relinking logic for SimpleFIN accounts and improved test coverage for related scenarios.

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Co-authored-by: Josh Waldrep <joshua.waldrep5+github@gmail.com>

app/models/simplefin_item/unlinking.rb

@@ -39,8 +39,10 @@ module SimplefinItem::Unlinking
           end
 
           # Legacy FK fallback: ensure any legacy link is cleared
-          if sfa.account_id.present?
-            sfa.update!(account: nil)
+          # NOTE: `SimplefinAccount#account_id` is the provider's external identifier.
+          # The legacy link is `Account.simplefin_account_id` (accessible via `sfa.account`).
+          if sfa.account.present?
+            sfa.account.update!(simplefin_account_id: nil)
           end
         end
       rescue => e