fix(tui): correct --skip-build hint and add TUI workspace install test

- Update the --skip-build pre-build hint in the dashboard startup path
  to use `npm install --workspace web && npm run build -w web` so users
  don't accidentally trigger a desktop rebuild by following the hint.

- Add test_tui_launch_install_uses_workspace_scope to assert that the
  TUI launch npm install carries --workspace ui-tui, covering the call
  site added in the prior commit.

hermes_cli/main.py

@@ -12412,7 +12412,7 @@ def cmd_dashboard(args):
         )
         if not (_dist_root / "index.html").exists():
             print(f"✗ --skip-build was passed but no web dist found at: {_dist_root}")
-            print("  Pre-build first:  cd web && npm install && npm run build")
+            print("  Pre-build first:  npm install --workspace web && npm run build -w web")
             print("  Or drop --skip-build to build automatically.")
             sys.exit(1)
         print(f"→ Skipping web UI build (--skip-build); using dist at {_dist_root}")