fix(frontend): revert scroll-to-bottom focus/tabIndex — prevents mobile keyboard

The Copilot review suggested adding terminal.focus() after scrollToBottom
and changing tabIndex to 0 for accessibility. Both changes inadvertently
open the soft keyboard on mobile when tapping the scroll-to-bottom button,
covering half the terminal. This is an intentional design decision: the
button scrolls without stealing focus so the keyboard stays closed.

Added inline comments explaining the rationale so reviewers understand
the intent.

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

Author: dorlugasigal

src/frontend/src/components/TerminalPane/TerminalPane.tsx

@@ -487,14 +487,19 @@ export function TerminalPane({ sessionId, active, visible, fontSize = 14 }: Term
   const scrollToBottom = useCallback(
     (e: React.MouseEvent) => {
       e.preventDefault();
+      // stopPropagation prevents the pane's onClick (which calls terminal.focus())
+      // from firing — intentional so tapping this button on mobile does NOT open
+      // the soft keyboard.
       e.stopPropagation();
       if (terminal) {
         programmaticScrollRef.current = true;
         terminal.scrollToBottom();
         programmaticScrollRef.current = false;
         wasAtBottomRef.current = true;
         setShowScrollBtn(false);
-        terminal.focus();
+        // NOTE: Do NOT call terminal.focus() here — on mobile devices that
+        // would open the soft keyboard, covering half the terminal. Users who
+        // want to type can tap the terminal area directly.
       }
     },
     [terminal],
@@ -528,7 +533,11 @@ export function TerminalPane({ sessionId, active, visible, fontSize = 14 }: Term
         <button
           className={styles.scrollToBottom}
           onClick={scrollToBottom}
-          tabIndex={0}
+          // tabIndex={-1}: intentionally removed from tab order so that
+          // tapping this button on mobile doesn't make it the active element
+          // and inadvertently open the soft keyboard. The button is still
+          // reachable via screen readers through its aria-label.
+          tabIndex={-1}
           aria-label="Scroll to bottom"
         >
           ↓