openai service and basic tables with migrations

db/migrations/20260102021529_wa_identity_map.sql

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+-- migrate:up
+create table wa_identity_map (
+  tenant_id uuid not null references tenants(id) on delete cascade,
+  wa_chat_id text not null,
+  woo_customer_id bigint not null,
+  created_at timestamptz not null default now(),
+  updated_at timestamptz not null default now(),
+  primary key (tenant_id, wa_chat_id)
+);
+
+-- migrate:down
+drop table if exists wa_identity_map;