feat(reports): record loading and unloading time per stop

The OCC report publishes total loading and unloading time and the other
activity left over from a station stay, but nothing recorded when handling
started or ended — the July 2026 seed had to write the figure into a
checkpoint note. Four nullable stamps now ride the stop's arrival row, which
is the row the staying-time report builds a stay from (a turnaround's
departure belongs to a different schedule).

Handling is unloading start to loading end, so a container stop reads as one
window and a bulk station that only loads or only unloads still reports its
half; other activity is the rest of the stay. Both stay NULL where nothing
was logged rather than collapsing to zero.

- station-staying-time: + loading/unloading and other activity per stop
- turnaround-cycle: + the same, summed over the cycle's stops
- loading-unloading (new): per train per station per period, so a week or
  month view is that train's average over its stops
- the stop/stay query moves to operations-classification, shared by both

apps/edr-freight-api/src/migrations/3690000000000-CheckpointHandlingTimes.ts

@@ -0,0 +1,41 @@
+import { MigrationInterface, QueryRunner } from "typeorm";
+
+/**
+ * Loading and unloading times, on the stop that already records the train
+ * standing at a station.
+ *
+ * The OCC report publishes, per train, "total loading and unloading time" and
+ * the "other activity" left over from the station stay. Nothing recorded when
+ * handling started or ended — the July 2026 seed had to write the figure into
+ * a checkpoint's note — so the staying-time report could only ever publish the
+ * whole stay.
+ *
+ * These four go on `train_checkpoint_events` rather than a table of their own:
+ * a stop is already one row there, keyed (schedule, sequence_no), and the
+ * arrival row is the one the staying-time report builds a stay from. All four
+ * are nullable — a stop where nobody logged the handling still reports its
+ * staying time, with the handling columns empty rather than zero.
+ */
+export class CheckpointHandlingTimes3690000000000 implements MigrationInterface {
+  name = "CheckpointHandlingTimes3690000000000";
+
+  public async up(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(`
+      ALTER TABLE freight.train_checkpoint_events
+        ADD COLUMN IF NOT EXISTS unloading_started_at timestamptz,
+        ADD COLUMN IF NOT EXISTS unloading_completed_at timestamptz,
+        ADD COLUMN IF NOT EXISTS loading_started_at timestamptz,
+        ADD COLUMN IF NOT EXISTS loading_completed_at timestamptz;
+    `);
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(`
+      ALTER TABLE freight.train_checkpoint_events
+        DROP COLUMN IF EXISTS unloading_started_at,
+        DROP COLUMN IF EXISTS unloading_completed_at,
+        DROP COLUMN IF EXISTS loading_started_at,
+        DROP COLUMN IF EXISTS loading_completed_at;
+    `);
+  }
+}