fix(seed): make UpsertIATADetails a true upsert

UpsertIATADetails was a plain UPDATE that silently affected zero rows
when the iata_codes row did not yet exist.  Adding a new IATA to the
config for the first time resulted in display_name, approx_lat, and
approx_lng remaining NULL.

Change the query to INSERT ... ON CONFLICT DO UPDATE so the row is
atomically created (if missing) or updated (if present), matching the
function's name and the pattern used by UpsertTransportScope.

db/queries/queries.sql

@@ -17,11 +17,12 @@ SELECT * FROM iata_codes WHERE iata = $1;
 SELECT * FROM iata_codes ORDER BY iata;
 
 -- name: UpsertIATADetails :exec
-UPDATE iata_codes SET
-    display_name = $2,
-    approx_lat   = $3,
-    approx_lng   = $4
-WHERE iata = $1;
+INSERT INTO iata_codes (iata, display_name, approx_lat, approx_lng)
+VALUES ($1, $2, $3, $4)
+ON CONFLICT (iata) DO UPDATE SET
+    display_name = EXCLUDED.display_name,
+    approx_lat   = EXCLUDED.approx_lat,
+    approx_lng   = EXCLUDED.approx_lng;
 
 -- ============================================================
 -- TRANSPORT CODES