feat: full dark mode with :root.dark and dark: classes

layout.css
- Change .dark → :root.dark so variable overrides match Tailwind's
  :root, :host specificity and actually take effect
- Add global dark mode styles for input/select/textarea elements

All .svelte files:
- bg-white → bg-white dark:bg-gray-100 (cards, tables, containers)
- text-white → text-white dark:text-gray-950 (button text)
- Add dark:bg-gray-950 to main page containers (dashboard, account,
  license-keys, proclamations, proclamations/[id])
- Add dark:border-gray-300 to bordered elements (cards, tables, forms)
- Add dark:bg-gray-200 to secondary backgrounds (table headers,
  address form, price badges)
- Add dark:hover:bg-gray-300 / dark:hover:bg-gray-700 to hover states
  (sidebar nav links, clear button, admin categories table)

src/routes/(protected)/+layout.svelte

@@ -29,7 +29,7 @@
 				href={link.href}
 				class="rounded px-3 py-1.5 text-sm font-medium transition-colors {isActive(link.href)
 					? 'bg-blue-50 text-blue-700'
-					: 'text-gray-600 hover:bg-gray-50 hover:text-gray-900'}"
+					: 'text-gray-600 hover:bg-gray-50 hover:text-gray-900 dark:hover:bg-gray-300 dark:hover:text-gray-100'}"
 			>
 				{link.label}
 			</a>
@@ -40,7 +40,7 @@
 					href="/admin"
 					class="rounded px-3 py-1.5 text-sm font-medium transition-colors {isActive('/admin')
 						? 'bg-blue-50 text-blue-700'
-						: 'text-gray-700 hover:bg-gray-50 hover:text-gray-900'}"
+						: 'text-gray-700 hover:bg-gray-50 hover:text-gray-900 dark:hover:bg-gray-300 dark:hover:text-gray-100'}"
 				>
 					Admin Panel
 				</a>
@@ -52,7 +52,7 @@
 								'/admin/' + model.slug
 							)
 								? 'bg-blue-50 text-blue-700'
-								: 'text-blue-600 hover:bg-gray-50 hover:text-blue-800'}"
+								: 'text-blue-600 hover:bg-gray-50 hover:text-blue-800 dark:hover:bg-gray-300 dark:hover:text-gray-100'}"
 						>
 							{model.displayName}
 						</a>