fix(reports): count container tonnage in exports and reports

Every SQL tonnage in the export datasets and report definitions used
`COALESCE(b.bulk_total_weight_tons, b.cargo_total_weight_vgm)`. COALESCE
falls through on NULL, never on 0 — and the portal booking wizard stores
`cargo_total_weight_vgm = 0` for container freight on purpose, because VGM
is captured per container line, not as a booking-level figure. So every
portal-created container booking reported as weighing nothing. The
backoffice wizard does store a booking-level total, so the same table holds
both shapes and the numbers looked erratic rather than uniformly zero.

Extract the resolver the TypeScript side already has three copies of
(bookingCargoTons, cargoTonsAndItems, totalVgmTons) into one SQL helper:
NULLIF both booking-level columns, then fall back to
SUM(booking_container.total_vgm_tons). Applied to the bookings and
train-schedules export datasets, the cargo-summary, contract-utilization and
booking-status-breakdown reports, and the intercity booking list.

On dev data this recovers 116 of 154 zero-weight container bookings and
raises live booking tonnage from 42,973 t to 61,424 t.

apps/edr-freight-api/src/modules/bookings/booking-tons.sql.spec.ts

@@ -0,0 +1,30 @@
+import { bookingTonsSql } from './booking-tons.sql';
+
+describe('bookingTonsSql', () => {
+  const sql = bookingTonsSql('b');
+
+  // The regression this exists for: a plain COALESCE stops at the portal's
+  // literal 0 for container bookings and reports them as weighing nothing.
+  it('treats a stored 0 as "no figure" on both booking-level columns', () => {
+    expect(sql).toContain('NULLIF(b.bulk_total_weight_tons, 0)');
+    expect(sql).toContain('NULLIF(b.cargo_total_weight_vgm, 0)');
+  });
+
+  it('falls back to the per-line container VGM, excluding soft-deleted lines', () => {
+    expect(sql).toContain('SUM(bc.total_vgm_tons)');
+    expect(sql).toContain('freight.booking_container bc');
+    expect(sql).toContain('bc.booking_id = b.id');
+    expect(sql).toContain('bc.deleted_at IS NULL');
+  });
+
+  it('never returns NULL, so callers may SUM it directly', () => {
+    expect(sql.trimEnd().endsWith('0)')).toBe(true);
+  });
+
+  it('rewrites every reference when embedded under another alias', () => {
+    const aliased = bookingTonsSql('bk');
+    expect(aliased).not.toMatch(/\bb\./);
+    expect(aliased).toContain('bk.cargo_total_weight_vgm');
+    expect(aliased).toContain('bc.booking_id = bk.id');
+  });
+});