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

test/readme-deployment-refresh.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+# Scope: validates backend unit tests and frontend production build for the README deployment refresh.
+
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+
+(
+  cd "$ROOT_DIR/backend"
+  go test ./...
+)
+
+(
+  cd "$ROOT_DIR/frontend"
+  npm ci
+  npm run build
+)