feat(share): add Share Collection cashier flow and fix Share Product accounting

- Add Share Collection screen under Cashier menu for cash pre-collection
  before share account activation; posts Dr Cash Vault, Cr Share Sundry,
  Cr Income GL entries with duplicate-collection guard
- Restore all 4 GL mappings (Assets, Liabilities, Income, Equity) in Share
  Product accounting step with pill-style savings-product UI
- Remove Multiples section from Share Product currency step; default
  Decimal Places to 2
- GET /cashier/sharecollection/:id endpoint for collection status check

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/core/shell/shell.component.html

@@ -725,6 +725,9 @@
       <button mat-menu-item tabindex="0" [routerLink]="['/cashier/cash-history']">
         <fa-icon icon="history" class="menu-item-icon"></fa-icon> Cash History
       </button>
+      <button mat-menu-item tabindex="0" [routerLink]="['/cashier/share-collection']">
+        <fa-icon icon="hand-holding-usd" class="menu-item-icon"></fa-icon> Share Collection
+      </button>
     </mat-menu>
 
     <mat-menu #depositsMenu="matMenu" class="deposits-mega-panel" [overlapTrigger]="false">