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)/(user)/license-keys/+page.svelte

@@ -4,13 +4,13 @@
 	let { data }: PageProps = $props();
 </script>
 
-<div class="flex h-full min-h-0 flex-col gap-6 p-6">
+<div class="flex h-full min-h-0 flex-col gap-6 p-6 dark:bg-gray-950">
 	<h1 class="text-2xl font-semibold text-gray-900">License Keys</h1>
 
 	{#if data.licenseKeys.length > 0}
-		<div class="overflow-x-auto rounded-lg border border-gray-200">
-			<table class="min-w-full divide-y divide-gray-200">
-				<thead class="bg-gray-50">
+		<div class="overflow-x-auto rounded-lg border border-gray-200 dark:border-gray-300">
+			<table class="min-w-full divide-y divide-gray-200 dark:divide-gray-300">
+				<thead class="bg-gray-50 dark:bg-gray-200">
 					<tr>
 						<th class="px-6 py-3 text-left text-xs font-medium uppercase tracking-wider text-gray-500">
 							Key
@@ -23,7 +23,7 @@
 						</th>
 					</tr>
 				</thead>
-				<tbody class="divide-y divide-gray-200 bg-white">
+				<tbody class="divide-y divide-gray-200 dark:divide-gray-300 bg-white dark:bg-gray-100">
 					{#each data.licenseKeys as key}
 						<tr>
 							<td class="whitespace-nowrap px-6 py-4 font-mono text-sm text-gray-900">