refactor: full-stack restructure with multi-tenancy, workspace management, and K8s diagnostics

- Add Workspace domain (entity, repository, service, handler, DTO)
- Add multi-tenant K8s client with tenant binding and quota management
- Add K8s diagnostics client (instance diagnostics)
- Add authorization middleware (authz package)
- Restructure frontend to feature-based architecture (features/)
- Add User Management page in configuration
- Add AccessDenied page and route guards
- Refactor shared components (form inputs, layout, UI)
- Update Tailwind config for new design system
- Add comprehensive documentation (docs/, tasks/, plans)
- Improve cluster service with better kubeconfig handling
- Add tests for crypto, config, helm client, tenant binding

.gitignore

@@ -60,4 +60,19 @@ redis_data/
 tmp/
 temp/
 *.tmp
+.fuse_hidden*
+
+# Debug scripts
+debug_*.py
+test_*.py
+
+# Next.js build output (including stale caches)
+frontend/.next*/
+frontend/next-env.d.ts
+
+# Compiled binary
+backend/ocdp-backend
+
+# IDE / AI temp
+.claude/