gui: update slash command hints to match ctl surface

The agent now routes all /commands to ctl. Update the autocomplete
hint list to reflect current ctl commands.

gui/main.qml

@@ -78,18 +78,6 @@ ApplicationWindow {
         }
     }
 
-    // --- Slash command definitions ---
-    readonly property var slashCommands: [
-        { name: "model",      desc: "Set model" },
-        { name: "backend",    desc: "Set backend" },
-        { name: "agent",      desc: "Switch agent" },
-        { name: "stop",       desc: "Stop current run" },
-        { name: "kill",       desc: "Kill session" },
-        { name: "new",        desc: "New session" },
-        { name: "compact",    desc: "Compact context" },
-        { name: "help",       desc: "Show help" }
-    ]
-
     // Sidebar visibility
     property bool sidebarVisible: true