chore: add multi-agent build pipeline (.claude/ agents, orchestrator, gates)

Adds crewli-architect, backend/frontend-implementer, test-writer subagents,
the /build-module orchestrator command, the PR merge-gate template, and a
permissions allow-list in settings.json. Documents the layer as
CLAUDE_CODE_TOOLING.md section 10. Implementer Edit/Write is allow-listed;
git push deliberately omitted so merge/push stay human.

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

.gitignore

@@ -84,3 +84,7 @@ apps/app/dist/**/*.map
 
 *storybook.log
 storybook-static
+
+# Python bytecode
+__pycache__/
+*.pyc