Run wp-cli as www-data instead of root; drop --allow-root

--allow-root was routing around wp-cli's own safety check rather than
addressing why root was there in the first place: docker exec defaults to
the container's root user because the image never sets a non-root user
for exec sessions — it was never about the actual web-facing attack
surface, which already runs as www-data (verified: php-fpm's worker
processes, the ones executing plugin/theme code for real requests, run as
uid 33, not root; only our own deliberate admin commands were root).

wp-config.php and the rest of wp-core are already owned by www-data (the
official entrypoint sets this up), so there's no actual reason for our
own commands to run as anything else. Verified: a full clean deploy and
a bookstore-core wp-cli command both work identically running as
www-data, no functional change, just removed an unnecessary privilege.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Makefile

@@ -22,12 +22,13 @@ ps:
 logs:
 	$(COMPOSE) logs -f
 
+# add -u root yourself for one-off root debugging (installing a package, etc.)
 shell:
-	$(COMPOSE) exec wordpress bash
+	$(COMPOSE) exec -u www-data wordpress bash
 
 # make wp ENV=staging ARGS="plugin list"
 wp:
-	$(COMPOSE) exec wordpress wp $(ARGS) --allow-root
+	$(COMPOSE) exec -u www-data wordpress wp $(ARGS)
 
 deploy:
 	./deploy/deploy.sh $(ENV)