ui: fix logs tab height and column toggle dropdown

- Make ModelLogsTab fill available vertical space instead of fixed h-80
- Add min-h-0 flex-1 to Logs Tabs.Content so height propagates
- Set closeOnSelect=false on column visibility checkbox items to keep
  the dropdown open while toggling multiple columns

ui-svelte/src/components/ActivityTable.svelte

@@ -354,6 +354,7 @@
               <DropdownMenu.CheckboxItem
                 checked={column.getIsVisible()}
                 onCheckedChange={(v) => column.toggleVisibility(!!v)}
+                closeOnSelect={false}
               >
                 {columnLabelMap[column.id] ?? column.id}
               </DropdownMenu.CheckboxItem>

ui-svelte/src/components/model/ModelLogsTab.svelte

@@ -21,6 +21,6 @@
   });
 </script>
 
-<div class="h-80">
+<div class="h-full">
   <LogPanel id={`model-${modelId}`} title="Model Logs" {logData} />
 </div>

ui-svelte/src/routes/ModelDetail.svelte

@@ -82,7 +82,7 @@
       </Tabs.Content>
 
       <!-- Logs -->
-      <Tabs.Content value="logs">
+      <Tabs.Content value="logs" class="min-h-0 flex-1">
         <ModelLogsTab modelId={modelId} />
       </Tabs.Content>