feat(accounting): redesign Migrate Opening Balances for clarity, point env at abc_bank tenant

- Replaces the flat, hard-to-scan opening-balances form with a stepped layout: branch pick, a
  clearly-explained contra account, a pinned Debit/Credit balance status (green "Balanced" vs red
  "Out of balance by X"), and account rows grouped by type with a mobile-responsive grid. No
  behavior change - same form controls, same validation, same submit flow.
- env.js: default/available tenant switched from default,socity_bank to abc_bank.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/assets/env.js

@@ -17,8 +17,8 @@
   window["env"]["apiVersion"] = '';
   window["env"]["apiActuator"] = '';
 
-  window["env"]["fineractPlatformTenantId"] = '';
-  window["env"]["fineractPlatformTenantIds"] = 'default,socity_bank';
+  window["env"]["fineractPlatformTenantId"] = 'abc_bank';
+  window["env"]["fineractPlatformTenantIds"] = 'abc_bank';
 
   window['env']['tenantLogoUrl'] = '';
   window['env']['tenantLogoUrlDark'] = '';