feat(ui) : add site colors, dark mode toggle and card styling improvements

- Site color field with color picker in create/edit modals
- Dark mode theme (mytheme-dark) with toggle in navbar
- Stronger site color visibility on cards (gradient, top border, badges)
- Bigger action buttons (btn-sm) on machine cards
- White card backgrounds with proper dark mode support

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

app/assets/app.css

@@ -56,6 +56,57 @@
   --noise: 0;
 }
 
+@plugin "daisyui/theme" {
+  name: "mytheme-dark";
+  default: false;
+  prefersdark: true;
+  color-scheme: dark;
+
+  /* Surfaces — dark blue-gray */
+  --color-base-100: oklch(22% 0.015 260);
+  --color-base-200: oklch(18% 0.012 260);
+  --color-base-300: oklch(28% 0.018 260);
+  --color-base-content: oklch(92% 0.005 260);
+
+  /* Primary — Malio blue, brighter for dark */
+  --color-primary: oklch(55% 0.18 262);
+  --color-primary-content: oklch(98% 0.005 262);
+
+  /* Secondary — refined lavender */
+  --color-secondary: oklch(72% 0.06 275);
+  --color-secondary-content: oklch(22% 0.03 275);
+
+  /* Accent — warm amber-orange */
+  --color-accent: oklch(72% 0.17 55);
+  --color-accent-content: oklch(20% 0.04 55);
+
+  /* Neutral — lighter slate for dark mode */
+  --color-neutral: oklch(75% 0.02 260);
+  --color-neutral-content: oklch(18% 0.01 260);
+
+  /* Semantic */
+  --color-info: oklch(62% 0.14 255);
+  --color-info-content: oklch(98% 0.005 255);
+  --color-success: oklch(65% 0.19 150);
+  --color-success-content: oklch(98% 0.005 150);
+  --color-warning: oklch(78% 0.15 70);
+  --color-warning-content: oklch(22% 0.05 70);
+  --color-error: oklch(62% 0.22 25);
+  --color-error-content: oklch(98% 0.005 25);
+
+  /* Geometry — same as light */
+  --radius-selector: 0.75rem;
+  --radius-field: 0.375rem;
+  --radius-box: 0.625rem;
+
+  --size-selector: 0.25rem;
+  --size-field: 0.25rem;
+
+  --border: 1px;
+  --depth: 1;
+  --noise: 0;
+}
+
 /* ─── Typography ─── */
 :root {
   --font-heading: 'Outfit', system-ui, sans-serif;
@@ -139,6 +190,18 @@ h1, h2, h3, h4, h5, h6,
   transition: box-shadow 0.2s ease, transform 0.2s ease;
 }
 
+.site-card {
+  background-color: oklch(100% 0 0);
+}
+
+[data-theme="mytheme-dark"] .site-card {
+  background-color: oklch(24% 0.015 260);
+}
+
+[data-theme="mytheme-dark"] .card {
+  border-color: oklch(30% 0.02 260 / 0.6);
+}
+
 .card:hover {
   box-shadow:
     0 4px 6px -1px oklch(22% 0.025 260 / 0.06),
@@ -153,6 +216,11 @@ h1, h2, h3, h4, h5, h6,
   border-bottom: 1px solid oklch(91% 0.015 260 / 0.5);
 }
 
+[data-theme="mytheme-dark"] .navbar-glass {
+  background: oklch(22% 0.015 260 / 0.85);
+  border-bottom-color: oklch(30% 0.02 260 / 0.5);
+}
+
 /* ─── Buttons ─── */
 .btn {
   font-family: var(--font-heading);