Keep the state layer off a disabled field trailing button

Plan step 36 audit. field.css's trailing button (clear, copy, reveal)
scales its state layer with the field's own icon size and doubles it as
the touch target, which the foundation's fixed-size interaction classes
cannot draw, and the hook stays data-md-field-button rather than a class
because datepicker and timepicker, not yet rewritten, still select it —
so it keeps its own declarations. It never hid the layer on a disabled
button, unlike every rewritten component's copy; it now does.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/css/components/field.css

@@ -165,7 +165,11 @@
         pointer-events: none;
     }
 
-    /* A trailing button — clear, copy, reveal — is an icon button: the icon in a 40px state layer. */
+    /* A trailing button — clear, copy, reveal — is an icon button: the icon in a state layer that
+       scales with the field's own icon size (40px at `md`, smaller at `sm`/`xs`), which the
+       foundation's fixed-size classes cannot draw; the layer doubles as the touch target, since it
+       already reaches 40px+ without a second pseudo. The hook stays `data-md-field-button` rather
+       than a class because datepicker and timepicker, not yet rewritten, still select it. */
     [data-md-field-button] {
         position: relative;
         display: grid;
@@ -203,6 +207,11 @@
         background-color: color-mix(in srgb, var(--md-sys-color-on-surface-variant) calc(var(--md-sys-state-pressed-state-layer-opacity) * 100%), transparent);
     }
 
+    [data-md-field-button]:disabled::before,
+    [data-md-field-button][aria-disabled='true']::before {
+        display: none;
+    }
+
     [data-md-field-affix] {
         flex: none;
         color: var(--md-sys-color-on-surface-variant);