fix(tui): tighten composer — status sits directly above input, overlays anchor to input

Three bugs rolled together, all in the composer area:

- StatusRule was measuring as 2 rows in Yoga due to a quirk with the
  complex nested <Text wrap="truncate-end"> content. Lock the outer box
  to height={1} so 'top' mode actually abuts the input instead of
  leaving a phantom blank row between them
- FloatingOverlays (slash completions, /model picker, /resume, /skills
  browser, pager) was anchored to the status box. In 'bottom' mode the
  status box moved away, so overlays vanished. Move the overlays into
  the input row (which is position:relative) so they always pop up
  above the input regardless of status position
- Drop the <Text> </Text> fallback in the sticky-prompt slot (only
  render a row when there's an actual sticky prompt to show) and
  collapse the now-unused Box column wrapping the input. Saves two
  rows of dead vertical space in the default layout

ui-tui/src/components/appChrome.tsx

@@ -187,7 +187,7 @@ export function StatusRule({
   const leftWidth = Math.max(12, cols - cwdLabel.length - 3)
 
   return (
-    <Box>
+    <Box flexShrink={0} height={1}>
       <Box flexShrink={1} width={leftWidth}>
         <Text color={t.color.bronze} wrap="truncate-end">
           {'─ '}