fix: refine presentation slides 2, 5 and 7

scripts/browser/presentation-staircase.cjs

@@ -0,0 +1,14 @@
+// Browser-side geometry contract, shared by standalone and embedded acceptance.
+module.exports = function staircaseFits() {
+ const els=[...document.querySelectorAll('#learning-loop .learning-loop>*')];
+ const b=els.map(e=>e.getBoundingClientRect());
+ const center=r=>({x:(r.left+r.right)/2,y:(r.top+r.bottom)/2});
+ const close=(a,b)=>Math.abs(a-b)<2;
+ return [[0,1,2],[4,5,6],[8,9,10]].every(([a,arrow,c])=>
+  close(center(b[a]).y,center(b[c]).y)&&close(center(b[a]).y,center(b[arrow]).y)&&
+  b[a].right<=b[arrow].left+2&&b[arrow].right<=b[c].left+2
+ )&&[[2,3,4],[6,7,8]].every(([a,arrow,c])=>
+  close(center(b[a]).x,center(b[c]).x)&&close(center(b[a]).x,center(b[arrow]).x)&&
+  b[a].bottom<=b[arrow].top+2&&b[arrow].bottom<=b[c].top+2
+ )&&els.filter(e=>e.tagName==='SPAN').every(e=>e.scrollWidth<=e.clientWidth+1);
+};