feat(ui): mobile polish — tab bar icons, server overlay, status text

Tab bar: replace plain Header strings with icon+label StackPanels
(≡ ↑ ↓ ⊙ ⊕); style TabStrip with UniformGrid so all five tabs share
the full width equally; center content and add touch padding. Icons
are visible only on mobile (IsMobile binding); desktop keeps text only.

Server settings overlay: dual layout for host/port/TLS input (vertical
on mobile: host full-width, port+TLS side by side) and for action
buttons (stacked full-width on mobile). Known-server list item shows
host on one line and tcp/ssl ports on the line below on mobile.

Connection status bar: simplify to "connesso" / "non connesso" —
remove the "a host:port" suffix from the connected state and
consolidate all disconnected/error/cert-changed states to conn.none.

src/App/ViewModels/MainWindowViewModel.Sync.cs

@@ -144,11 +144,11 @@ public partial class MainWindowViewModel
                 _client.Disconnected += _ => Dispatcher.UIThread.Post(() =>
                 {
                     IsConnected = false;
-                    ConnectionStatus = Loc.Tr("conn.disconnected");
+                    ConnectionStatus = Loc.Tr("conn.none");
                 });
                 IsConnected = true;
                 _autoReconnect = true;
-                ConnectionStatus = $"{Loc.Tr("conn.connectedto")} {host}:{port}{(UseSsl ? " (TLS)" : "")}";
+                ConnectionStatus = Loc.Tr("conn.connectedto");
             }
 
             if (_account is null || _doc is null)
@@ -186,13 +186,13 @@ public partial class MainWindowViewModel
         catch (CertificatePinMismatchException ex)
         {
             IsConnected = false;
-            ConnectionStatus = Loc.Tr("conn.certchanged");
+            ConnectionStatus = Loc.Tr("conn.none");
             StatusMessage = ex.Message;
         }
         catch (Exception ex)
         {
             IsConnected = _client?.IsConnected == true;
-            ConnectionStatus = IsConnected ? ConnectionStatus : Loc.Tr("conn.error");
+            ConnectionStatus = IsConnected ? ConnectionStatus : Loc.Tr("conn.none");
             StatusMessage = $"Errore: {ex.Message}";
         }
         finally