minor db index work

sql/initial_schema.sql

@@ -235,6 +235,7 @@ CREATE TABLE IF NOT EXISTS public.store_locations (
     store_id BIGINT REFERENCES public.stores(store_id) ON DELETE CASCADE,
     address_id BIGINT NOT NULL REFERENCES public.addresses(address_id) ON DELETE CASCADE,
     created_at TIMESTAMPTZ DEFAULT now() NOT NULL,
+    UNIQUE(store_id, address_id),
     updated_at TIMESTAMPTZ DEFAULT now() NOT NULL
 );
 COMMENT ON TABLE public.store_locations IS 'Stores physical locations of stores with geographic data for proximity searches.';