Support schedule trip variants

backend/migrations/006_schedule_trip_variants.sql

@@ -0,0 +1,26 @@
+-- Per-departure metadata for partial, via-stop, and calendar-specific trips.
+-- Existing clients can continue to use departure_times; trips is the richer source.
+ALTER TABLE schedules
+    ADD COLUMN IF NOT EXISTS trips JSONB NOT NULL DEFAULT '[]'::jsonb;
+
+UPDATE schedules
+SET trips = (
+    SELECT COALESCE(
+        jsonb_agg(
+            jsonb_build_object(
+                'departureTime', to_char(departure_time, 'HH24:MI:SS'),
+                'startStopId', NULL,
+                'endStopId', NULL,
+                'viaStopIds', '[]'::jsonb,
+                'daysOfWeek', '[]'::jsonb,
+                'exceptDaysOfWeek', '[]'::jsonb,
+                'note', ''
+            )
+            ORDER BY departure_time
+        ),
+        '[]'::jsonb
+    )
+    FROM unnest(departure_times) AS expanded_departures(departure_time)
+)
+WHERE trips = '[]'::jsonb
+  AND departure_times IS NOT NULL;