fix(saas): migration idempotency fixes + SCHEMA_VERSION bump to 14

- Add IF NOT EXISTS to accounts_template_assignment ALTER COLUMN
- Add IF NOT EXISTS to webhooks CREATE INDEX statements
- Add created_at/updated_at columns + ON CONFLICT DO NOTHING to industry templates
- Bump SCHEMA_VERSION 13→14 to force migration re-run on existing DB

crates/zclaw-saas/migrations/20260403000002_webhooks.sql

@@ -23,6 +23,6 @@ CREATE TABLE IF NOT EXISTS webhook_deliveries (
     created_at TIMESTAMPTZ NOT NULL DEFAULT now()
 );
 
-CREATE INDEX idx_webhook_subscriptions_account ON webhook_subscriptions(account_id);
-CREATE INDEX idx_webhook_subscriptions_events ON webhook_subscriptions USING gin(events);
-CREATE INDEX idx_webhook_deliveries_pending ON webhook_deliveries(subscription_id) WHERE delivered_at IS NULL;
+CREATE INDEX IF NOT EXISTS idx_webhook_subscriptions_account ON webhook_subscriptions(account_id);
+CREATE INDEX IF NOT EXISTS idx_webhook_subscriptions_events ON webhook_subscriptions USING gin(events);
+CREATE INDEX IF NOT EXISTS idx_webhook_deliveries_pending ON webhook_deliveries(subscription_id) WHERE delivered_at IS NULL;