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.component.html

@@ -88,6 +88,22 @@
       </div>
     </a>
 
+    <!-- Migrate Cash Denomination -->
+    <a
+      class="acc-card"
+      [routerLink]="['migrate-cash-denomination']"
+      *mifosxHasPermission="'READ_JOURNALENTRY'"
+      #migrateCashDenomination
+    >
+      <div class="acc-card__icon amber"><i class="fas fa-coins"></i></div>
+      <div class="acc-card__info">
+        <span class="acc-card__title">Migrate Cash Denomination</span>
+        <span class="acc-card__desc">
+          Count the vault opening cash into notes and coins, and open the first business day
+        </span>
+      </div>
+    </a>
+
     <!-- Chart of Accounts -->
     <a class="acc-card" [routerLink]="['chart-of-accounts']" *mifosxHasPermission="'READ_GLACCOUNT'" #chartofAccounts>
       <div class="acc-card__icon blue"><i class="fas fa-sitemap"></i></div>