feat(maestro): move activity indicator into scroll area

The "Running 1m ..." status now sits at the tail of the chat
history instead of pinned above the input, matching Claude Code's
placement.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/styles.css

@@ -2318,9 +2318,7 @@ input.leaf-rename:focus {
   gap: var(--sp-2);
   min-height: 30px;
   padding: var(--sp-1) var(--sp-3);
-  border-top: 1px solid var(--border);
   color: var(--muted);
-  background: var(--surface-2);
   font-size: var(--fs-11);
   font-variant-numeric: tabular-nums;
 }