plasmoid: folder picker for new sessions, fix chat offset encoding

- New session button opens a FolderDialog to choose the working directory before creating the session.

- Fix chat truncation: use toUtf8().size() for offset tracking to match the server byte-based offsets. QString::size() (UTF-16 code units) caused drift on non-ASCII characters, leading to stalled output.

plasmoid/contents/ui/main.qml

@@ -24,6 +24,16 @@ PlasmoidItem {
         }
     }
 
+    FolderDialog {
+        id: newSessionFolderDialog
+        title: "Choose working directory for new session"
+        currentFolder: dbus.activeCwd ? "file://" + dbus.activeCwd : StandardPaths.writableLocation(StandardPaths.HomeLocation)
+        onAccepted: {
+            let path = selectedFolder.toString().replace("file://", "")
+            dbus.createSession(path)
+        }
+    }
+
     // On the desktop (Planar), the widget has plenty of room so Plasma will
     // automatically use fullRepresentation.  In a panel, the available space
     // is smaller than switchWidth/switchHeight so compactRepresentation is used.
@@ -122,7 +132,7 @@ PlasmoidItem {
 
             PlasmaComponents.ToolButton {
                 icon.name: "list-add"
-                onClicked: dbus.createSession("")
+                onClicked: newSessionFolderDialog.open()
                 PlasmaComponents.ToolTip { text: "New session" }
             }
         }

plasmoid/plugin/olliedbusclient.cpp

@@ -304,7 +304,7 @@ void OllieDBusClient::onChatUpdated(const QString &session_id, qlonglong offset,
     // Append directly from the signal — no need to poll
     if (offset == m_chatOffset) {
         m_chatText += new_text;
-        m_chatOffset += new_text.size();
+        m_chatOffset += new_text.toUtf8().size();
         emit chatTextChanged();
     } else {
         // Offset mismatch — do a full fetch