fix: prevent composer action bar from overlaying text field

Change the bottom action bar from absolute positioning to normal
document flow so it sits below the editable area instead of floating
on top. Reduce editable bottom padding since buttons no longer overlap.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/renderer/styles.css

@@ -145,7 +145,7 @@ body {
   min-height: 52px;
   max-height: 200px;
   overflow-y: auto;
-  padding: 10px 48px 10px 16px;
+  padding: 10px 16px 4px 16px;
   font-size: 14px;
   line-height: 1.6;
   color: #f4f4f5;