fix(ui): unify Session navigation and restore uniform tab borders

docs/guida-utente.md

@@ -7,7 +7,7 @@ the end of this page.
 ## Before creating a session
 
 An administrator must have selected a workspace and configured the installation-wide provider,
-model, and thinking settings. The New session form deliberately asks only for the question.
+model, and thinking settings. The new-question form deliberately asks only for the question.
 
 The workspace is a pinned Git revision. A subsequent workspace update cannot alter a session
 already created from an earlier revision. If a workspace cannot reach its configured runtime DWH,
@@ -15,7 +15,9 @@ new sessions are refused before any session state is written.
 
 ## Create and review a session
 
-1. Sign in and select **New session**.
+1. Sign in and select **Session** (**Sessione** in Italian). If a session is already
+   open and unfinished, this returns to it without restarting it. Otherwise it
+   opens a new question; no session is created until you submit that question.
 2. Enter a precise business question, including the relevant time period and desired output. For
    example: “List patients discharged in the last 30 days, with ward and discharge date.”
 3. Review each gate and make the decision requested by the widget. A choice with a decision payload