Stop the kitten measuring the size it shrank itself to

The mascot shrinks a step when it yields to a card, and the overlap test read
getBoundingClientRect, which reports the scaled box. So a card resting at the
mascot's edge drove a loop: overlap, shrink, no overlap, grow, overlap again,
every poll tick.

Measure the layout box instead — centre plus offsetWidth/offsetHeight, which
the yield transform doesn't move. Hysteresis would have hidden the pulsing;
this removes the path that caused it.

Claude-Session: https://claude.ai/code/session_01GJHNvirh7Hzhc9RL3HAvz7

web/src/components/Companion/useCardOverlap.ts

@@ -24,6 +24,21 @@ export interface CardOverlap {
   modal: boolean
 }
 
+// The mascot shrinks a step when it yields (.petal-companion-faded), and
+// getBoundingClientRect reports the *scaled* box. Measuring that lets the
+// mascot shrink out of its own overlap test: it yields, stops overlapping,
+// wakes back up, overlaps again — pulsing forever against a card that sits just
+// at its edge. The layout box doesn't move when it yields, so measure that. The
+// transform origin is the centre, so it's the visual centre ± the layout size.
+function layoutRect(el: HTMLElement) {
+  const r = el.getBoundingClientRect()
+  const halfW = el.offsetWidth / 2
+  const halfH = el.offsetHeight / 2
+  const cx = (r.left + r.right) / 2
+  const cy = (r.top + r.bottom) / 2
+  return { left: cx - halfW, right: cx + halfW, top: cy - halfH, bottom: cy + halfH }
+}
+
 // Reports what, if anything, the mascot should yield to at the given element.
 // Used to fade the corner mascot out of the way when a card or panel reaches
 // into its corner, so nothing is ever hidden (or made unclickable) by the
@@ -37,7 +52,7 @@ export function useCardOverlap(ref: RefObject<HTMLElement | null>): CardOverlap
     const check = () => {
       const el = ref.current
       if (!el) return
-      const r = el.getBoundingClientRect()
+      const r = layoutRect(el)
       const hits = (selector: string) => {
         for (const other of document.querySelectorAll(selector)) {
           const b = other.getBoundingClientRect()