feat(cashier): full double-entry journal view + Excel export for Cash/Clearing/Transfer Summary

Transaction Details now renders each voucher as a paired Dr/Cr journal entry with a
derived contra account and a Balanced status chip, so both sides of a transaction are
visible at a glance for reconciliation. Adds a shared cashier-export.ts (mirrors the
Investment module's exporter) and an Export to Excel button producing a Summary +
Transaction Details workbook, plus a Branch Breakup sheet for Head Office consolidated view.

src/app/cashier/cash-clearing-transfer-summary/cash-clearing-transfer-summary.component.scss

@@ -71,3 +71,68 @@
     background: #eff6ff;
   }
 }
+
+// Both journal lines of one voucher share a tint and sit flush against each other (no dotted
+// divider between them) so the pair reads as a single entry; a hairline separates one voucher's
+// pair from the next.
+.cctr-journal-row {
+  &--first td {
+    border-bottom: none;
+    padding-bottom: 4px;
+  }
+
+  &--second td {
+    border-top: none;
+    padding-top: 4px;
+    border-bottom: 1px solid #e2e8f0;
+  }
+
+  &--first,
+  &--second {
+    &:hover td {
+      background: #f8fafc;
+    }
+  }
+}
+
+.cctr-drcr {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 28px;
+  padding: 1px 8px;
+  border-radius: 6px;
+  font-size: 11px;
+  font-weight: 800;
+  letter-spacing: 0.03em;
+
+  &--dr {
+    background: #eff6ff;
+    color: #1d4ed8;
+    border: 1px solid #bfdbfe;
+  }
+
+  &--cr {
+    background: #f0fdf4;
+    color: #15803d;
+    border: 1px solid #bbf7d0;
+  }
+}
+
+.cctr-contra {
+  color: #64748b;
+  font-style: italic;
+}
+
+.cctr-balanced-chip {
+  display: inline-flex;
+  align-items: center;
+  padding: 3px 10px;
+  border-radius: 999px;
+  font-size: 11px;
+  font-weight: 700;
+  background: #f0fdf4;
+  color: #15803d;
+  border: 1px solid #bbf7d0;
+  white-space: nowrap;
+}