Bound a text field's width from medium

M3 § Text Fields, Behaviour: compact may let a field span full width, but
medium and expanded must bound it — "never let it span the full width of a
large screen". Nothing in the package capped a field (plan step 24, audit
docs/audits/m3-alignment/inputs.md § Missing). From `medium` a field now stops
at 40rem — the site names no number, so the header says where this one comes
from — which a `max-w-*` class beats and `full` takes off. The search bar
already carries M3's own 720px.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/css/components/field.css

@@ -42,6 +42,20 @@
         min-width: 0;
     }
 
+    /* M3 § Text Fields, Behaviour: "compact breakpoints can let a text field span full width;
+     * medium/expanded should bound it with flexible margins/other containers — never let it span the
+     * full width of a large screen." The site names no number, so 40rem is this package's: it is
+     * under half the `large` class's 1200px, a little over the `expanded` class's half, and holds
+     * about the 70 characters body-large reads best at. It is a ceiling, not a width — a narrower
+     * pane still gets a narrower field. A `max-w-*` class from the call site beats it, because
+     * utilities come after this layer, and `full` takes it off for a field that really is the width
+     * of its pane (a search-and-filter row, an editor). Below `medium` nothing is bounded. */
+    @media (width >= 37.5rem) {
+        .field:not([data-full]) {
+            max-width: 40rem;
+        }
+    }
+
     /* A filled field's resting indicator line is on-surface-variant, where an outline is outline. */
     .field[data-variant="filled"] {
         --field-edge: var(--md-sys-color-on-surface-variant);