fix: fn_vehicle_trips takes bigint (domain.vehicles.vehicle_id is bigserial)

PG function overloading is type-strict: integer→bigint isn't implicit. The
prior signature (integer, date) didn't match callers passing vehicle_id
directly. Also prepends a DROP for the integer-signature in case the
previous migration ran and left a now-orphan function around.

db/migrations/20260601000019_fn_vehicle_trips.sql

@@ -33,8 +33,13 @@
 -- Falls back to movement-only segmentation (has_acc_data=false in the
 -- response) when every position for the day has acc_state IS NULL.
 
+-- Drop any prior signature; the function identity is (name + arg types),
+-- so a CREATE OR REPLACE with a different arg type would create a sibling.
+DROP FUNCTION IF EXISTS serve.fn_vehicle_trips(integer, date);
+DROP FUNCTION IF EXISTS serve.fn_vehicle_trips(bigint, date);
+
 CREATE OR REPLACE FUNCTION serve.fn_vehicle_trips(
-    p_vehicle_id integer,
+    p_vehicle_id bigint,
     p_date_eat   date
 ) RETURNS jsonb
 LANGUAGE plpgsql STABLE
@@ -385,4 +390,5 @@ $fn$;
 
 -- migrate:down
 
+DROP FUNCTION IF EXISTS serve.fn_vehicle_trips(bigint, date);
 DROP FUNCTION IF EXISTS serve.fn_vehicle_trips(integer, date);