clean up preview

app.py

@@ -67,10 +67,12 @@ def _summarize_columns(df, preview_max=VAR_PREVIEW_MAX):
         s = df[col]
         dtype = str(s.dtype)
         ex = pd.Series(s.astype(object)).dropna().astype(str).head(preview_max).tolist()
-        preview = ", ".join(ex) if ex else "—"
-        if len(preview) > 50:
+        preview = ", ".join(ex) if ex else "(no values)"
+        if len(preview) > 47:
             preview = preview[:47] + "..."
-        lbl = f"{col} · {dtype} · e.g. {preview}"
+        elif preview != "(no values)":
+            preview = preview + "..."
+        lbl = f"{col} · {dtype} · {preview}"
         choices.append((lbl, col))
     return choices