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/app/accounting/migrate-opening-balances/migrate-opening-balances.component.ts

@@ -16,6 +16,7 @@ import {
   ReactiveFormsModule
 } from '@angular/forms';
 import { ActivatedRoute, Router, RouterLink } from '@angular/router';
+import { MatIconModule } from '@angular/material/icon';
 
 /** Custom Services */
 import { AccountingService } from '../accounting.service';
@@ -41,7 +42,8 @@ import { STANDALONE_SHARED_IMPORTS } from 'app/standalone-shared.module';
   imports: [
     ...STANDALONE_SHARED_IMPORTS,
     GlAccountDisplayComponent,
-    CurrencyPipe
+    CurrencyPipe,
+    MatIconModule
   ]
 })
 export class MigrateOpeningBalancesComponent implements OnInit, AfterViewInit {