fix: mobile goal UX — bottom-sheet dialog, keyboard-safe target button, capacitor safe-top for overlays

- the goal dialog renders as the shared MobileOverlayPanel bottom sheet
  on mobile instead of a centered dialog
- tapping the target button to ARM keeps the soft keyboard open (the next
  message is the objective; same guard as the attachment/mic buttons),
  while opening the manage sheet lets the keyboard close as usual
- capacitor: bottom-sheet overlays cap their height by the keyboard inset
  AND the top safe area — with the keyboard raised while typing inside a
  sheet, 100dvh does not shrink (native resize is off) and the panel could
  slide under the notch/status bar; applies to every MobileOverlayPanel

packages/ui/src/components/chat/SessionGoalButton.tsx

@@ -76,6 +76,20 @@ export const SessionGoalButton: React.FC<SessionGoalButtonProps> = React.memo(({
       type="button"
       className={cn(footerIconButtonClass, colorClass)}
       onClick={handleClick}
+      // Same guard as PermissionAutoAcceptButton, but only for the ARM
+      // toggle: arming happens mid-typing (the next message IS the
+      // objective), so that tap must not dismiss the soft keyboard or
+      // trigger the Android keyboard-close relayout that moves the button
+      // before the click lands. Opening the manage sheet (goal exists) is a
+      // context switch — there the keyboard should close as usual.
+      onMouseDown={(event) => {
+        if (!goal) event.preventDefault();
+      }}
+      onPointerDownCapture={(event) => {
+        if (!goal && event.pointerType === 'touch') {
+          event.preventDefault();
+        }
+      }}
       aria-label={label}
       aria-pressed={isEngaged}
       {...(withTooltip ? {} : { title: label })}