fix: only add borderless css when not published (#3066)

## 📝 Summary

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There is a bad bug when you're in app view, since the borders are
removed, so hovering over the cell will cause borders to be re-added.
Borderless view is not needed in 'present' or 'view' mode.

## 🔍 Description of Changes

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## 📋 Checklist

- [X] I have read the [contributor
guidelines](https://github.com/marimo-team/marimo/blob/main/CONTRIBUTING.md).
- [ ] For large changes, or changes that affect the public API: this
change was discussed or approved through an issue, on
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- [ ] I have added tests for the changes made.
- [X] I have run the code and verified that it works as expected.

## 📜 Reviewers

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@akshayka OR @mscolnick

Author: Light2Dark

frontend/src/components/editor/Cell.tsx

@@ -421,7 +421,7 @@ const CellComponent = (
     stopped: stopped,
     disabled: cellConfig.disabled,
     stale: status === "disabled-transitively",
-    borderless: isMarkdownCodeHidden,
+    borderless: isMarkdownCodeHidden && editing,
   });
 
   const HTMLId = HTMLCellId.create(cellId);

frontend/src/components/editor/renderers/vertical-layout/vertical-layout.tsx

@@ -259,12 +259,13 @@ const VerticalCell = memo(
     const kioskFull = kiosk && mode !== "present";
 
     const isPureMarkdown = new MarkdownLanguageAdapter().isSupported(code);
+    const published = !showCode && !kioskFull;
     const className = cn("Cell", "hover-actions-parent empty:invisible", {
-      published: !showCode && !kioskFull,
+      published: published,
       interactive: mode === "edit",
       "has-error": errored,
       stopped: stopped,
-      borderless: isPureMarkdown,
+      borderless: isPureMarkdown && !published,
     });
 
     const HTMLId = HTMLCellId.create(cellId);