Fix buttons needing several clicks: stop control-bearing panels drifting

Save Configuration and Run API Check often ignored a click. The Python
handler was never at fault — it saves correctly on one click. The cause
was in the browser: the ambient float3d loop runs on every surface in
SURFACES, which includes [class*="st-key-ups_panel"], so the panel
holding the buttons carried a perpetual inline transform
(translateZ + rotateX, repeat: Infinity).

Measured on the running app: the Save button drifted 7.4px horizontally
and 4.3px vertically, continuously. A click only fires when mousedown
and mouseup land on the same element, so the moving button silently
swallowed clicks — Playwright could not click it at all, reporting
"element is not stable" across 56 retries in 30s.

motion_runtime already stated this rule for buttons ("a button that
moves under the cursor is a button that gets mis-clicked"); it just
never applied it to the surface carrying the button. Adds canDrift() —
a stricter sibling of canMove() — and gates float3d, tilt3d and the
.ups-ev depth wave on it. Entrance animations are untouched: they are
finite and settle. Presentation-only surfaces still float, tilt and
catch the sheen, so the design is unchanged.

After: all four buttons measure 0.0px drift and save on one click.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app/ui/motion_runtime.py

@@ -101,6 +101,27 @@ _DRIVER = r"""
     return true;
   }
 
+  // Perpetual motion is a stricter test than canMove.
+  //
+  // A `click` fires only when mousedown and mouseup land on the SAME element.
+  // A surface that drifts for as long as it lives — or turns under the
+  // pointer — moves every control it contains out from under the cursor
+  // between those two events, so clicks are silently swallowed and the user
+  // has to stab at the button several times before one lands. That is the
+  // same rule the button handler further down already states ("a button that
+  // moves under the cursor is a button that gets mis-clicked"); it just has
+  // to apply to the surface CARRYING the button, not only to the button.
+  //
+  // Entrance animations are deliberately exempt: they are finite and settle,
+  // so the arrival choreography is unchanged. Only never-ending motion is
+  // withheld, and only from surfaces that actually hold controls — a KPI
+  // tile or a verdict card still floats and tilts exactly as before.
+  var CONTROLS = 'button, input, select, textarea, a[href], [role="button"], ' +
+                 '[role="tab"], [role="option"], [contenteditable="true"]';
+  function canDrift(el) {
+    return canMove(el) && !el.querySelector(CONTROLS) && !el.matches(CONTROLS);
+  }
+
   // ── Depth ────────────────────────────────────────────────────────────
   // A translateZ only reads as depth when an ancestor carries a
   // perspective, and a perspective — like a transform — makes that
@@ -132,7 +153,7 @@ _DRIVER = r"""
   // long as the node lives, so nothing else may clear it. Anything that wants
   // the transform (hover, press, tilt) pauses this first and resumes after.
   function float3d(el, i) {
-    if (!canMove(el)) return;
+    if (!canDrift(el)) return;
     depthParent(el);
     el.style.transformStyle = 'preserve-3d';
     var ph = (i % 5) / 5;
@@ -158,6 +179,9 @@ _DRIVER = r"""
   // Pointer tilt. Hands over from the float and hands back on leave, because
   // two animations writing the same transform component fight each other.
   function tilt3d(el, max) {
+    // Guarded here rather than at each call site so no future caller can
+    // reintroduce a control-bearing surface that moves under the pointer.
+    if (!canDrift(el)) return;
     var frame = 0;
     el.addEventListener('pointerenter', function () { holdFloat(el); });
     el.addEventListener('pointermove', function (e) {
@@ -342,7 +366,9 @@ _DRIVER = r"""
     root.querySelectorAll('.ups-ev').forEach(function (el, i) {
       if (el.dataset.upsD) return;
       el.dataset.upsD = '1';
-      if (!canMove(el)) return;
+      // repeat: Infinity below — same rule as float3d: an entry that never
+      // settles must not be carrying anything clickable.
+      if (!canDrift(el)) return;
       depthParent(el);
       el.style.transformStyle = 'preserve-3d';
       el.__upsFloat = M.animate(el, {