fix: anchor tile preview to bottom so newest terminal content is visible

Previously the <pre> snapshot floated to the top of .tile-body — when
content overflowed, the oldest lines showed and newest were clipped.
Now .tile-body pre is position:absolute;bottom:0 so overflow clips
from the top and the lower-left corner (newest content) is always shown.

frontend/style.css

@@ -214,6 +214,13 @@ body {
   position: relative;
 }
 
+.tile-body pre {
+  position: absolute;
+  bottom: 0;
+  left: 0;
+  right: 0;
+}
+
 .tile-pre {
   position: absolute;
   inset: 0;