fix(themes): WCAG contrast audit for nucleo

Palette tokens lifted to AA on bg-card (#eedbb8):
- --warning (#a88020 → #7a5b0e): 2.68 → 4.64
- --border  (#b89a69 → #765a38): 1.97 → 4.70 (darker bronze, 3:1 UI on
  all bg variants including bg-player)
- --text-muted (#8c7356 → #6b5636): 3.29 → 5.14
- --positive  (#587838 → #3e5820): 3.72 → 5.90

Component override for column resize grip (default --ctp-surface1 is
1.08:1 on bg-card, invisible on this warm cream palette) — switch to
--border (4.70:1) with 2px width for a perceptible bronze grip.

Warm brass/aged-parchment palette preserved.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/styles/theme.css

@@ -724,11 +724,11 @@
   --accent-glow: rgba(122, 82, 24, 0.30);
   --text-primary: #2c1e10;
   --text-secondary: #5a3e20;
-  --text-muted: #8c7356;
-  --border: #b89a69;
+  --text-muted: #6b5636;
+  --border: #765a38;
   --border-subtle: #dfc08f;
-  --positive: #587838;
-  --warning: #a88020;
+  --positive: #3e5820;
+  --warning: #7a5b0e;
   --danger: #a03828;
 }
 
@@ -776,6 +776,14 @@
   box-shadow: 0 2px 5px rgba(44, 30, 16, 0.25), inset 0 1px 0 rgba(255, 255, 255, 0.4);
 }
 
+/* Column resize grip — default --ctp-surface1 (#f5e4c3) on bg-card (#eedbb8)
+   is 1.08:1 (invisible on this warm cream palette). Use --border (#765a38,
+   4.70:1) to get a perceptible bronze grip that matches the brass accents. */
+[data-theme='nucleo'] .col-resize-handle::after {
+  background: var(--border);
+  width: 2px;
+}
+
 /* ─── Psychowave — Synthwave / Retrowave ─── */
 [data-theme='psychowave'] {
   color-scheme: dark;