feat(ui): ensure cross-platform one-click setup and default Showcase UI routing

- Add explicit root route (/) in server.py to guarantee Showcase UI is served by default, routing /admin to the Admin Debug Console
- Enhance dynamic Angular dist detection across multiple standard output paths
- Add automated Node.js/npm detection and installation fallbacks to start scripts and installers across macOS, Linux, and Windows
- Automatically build Showcase UI when launching via start.sh, start.bat/start.ps1, or artemis ui if frontend artifacts are missing
- Add Node.js / npm and Showcase UI status inspection rows to artemis doctor
- Support artemis mcp --install for one-click IDE integration and add make build-ui target

.gitignore

@@ -81,6 +81,7 @@ data_engine.db
 data_engine.db-journal
 .ipc_port
 .ls_address
+.jetski_ls_address
 
 # Environment & Secrets
 .env