feat(savings,shares): bidirectional savings/share account linking, new Migrate Cash Denomination screen

- Savings account creation shows a required "Default Share Account" picker once Share Linking is
  enabled, populated from the client's active share accounts; submits shareAccountId alongside it.
- Fixes a real data-loss bug on Share Account creation: the Charges step re-seeded its table from
  the product's default charges on every ngOnChanges firing (e.g. stepping back to Details and
  forward again), silently discarding a charge the clerk had already added, edited, or removed - a
  pristine guard existed for exactly this but wasn't checked in ngOnChanges. Now it is.
- Removes the hard "required" on Share Account creation's Default Savings Account field, matching
  the backend now accepting a share account with no linked savings account.
- New /accounting/migrate-cash-denomination screen: counts a branch's opening cash into notes and
  coins, checks it against (or defines, if unset) the Cash GL account's balance, and opens the
  branch's first business day with that same count - the vault-side counterpart to Migrate Opening
  Balances, kept under Accounting rather than Branch Ops/Cashier so it isn't reachable by mistake.

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

src/app/accounting/accounting-routing.module.ts

@@ -25,6 +25,7 @@ import { CreateFinancialActivityMappingComponent } from './financial-activity-ma
 import { ViewFinancialActivityMappingComponent } from './financial-activity-mappings/view-financial-activity-mapping/view-financial-activity-mapping.component';
 import { EditFinancialActivityMappingComponent } from './financial-activity-mappings/edit-financial-activity-mapping/edit-financial-activity-mapping.component';
 import { MigrateOpeningBalancesComponent } from './migrate-opening-balances/migrate-opening-balances.component';
+import { MigrateCashDenominationComponent } from './migrate-cash-denomination/migrate-cash-denomination.component';
 import { ChartOfAccountsComponent } from './chart-of-accounts/chart-of-accounts.component';
 import { CreateGlAccountComponent } from './chart-of-accounts/create-gl-account/create-gl-account.component';
 import { ViewGlAccountComponent } from './chart-of-accounts/view-gl-account/view-gl-account.component';
@@ -185,6 +186,14 @@ const routes: Routes = [
             currencies: CurrenciesResolver
           }
         },
+        {
+          path: 'migrate-cash-denomination',
+          component: MigrateCashDenominationComponent,
+          data: { title: 'Migrate Cash Denomination', breadcrumb: 'Migrate Cash Denomination' },
+          resolve: {
+            offices: OfficesResolver
+          }
+        },
         {
           path: 'chart-of-accounts',
           data: { title: 'Chart of Accounts', breadcrumb: 'Chart of Accounts' },