fix: replace CSS variable inversion with standard Tailwind dark: classes

The :root.dark CSS variable inversion caused contrast problems -
text-gray-900 and bg-gray-950 both became light in dark mode, making
text invisible on backgrounds.

Fix:
- Remove :root.dark { --color-gray-*: ... } block from layout.css
- Change :root.dark selector to .dark for form element styles
- Add standard Tailwind dark: classes throughout every .svelte page
  - dark:bg-gray-950 (page backgrounds)
  - dark:bg-gray-900 (card/surface backgrounds)
  - dark:bg-gray-800 (table headers, elevated surfaces, active nav links)
  - dark:bg-gray-700 (primary buttons)
  - dark:text-gray-100 (primary text)
  - dark:text-gray-300 (secondary text, labels)
  - dark:text-gray-400 (muted text, inactive nav links, links)
  - dark:border-gray-700 (borders)
  - dark:border-gray-600 (input borders)
  - dark:hover:bg-gray-800 (sidebar hover)
  - dark:hover:bg-gray-600 (button hover)
  - dark:prose-invert (rich text content)
- TopBar: full dark mode support (bg, links, toggle button)
- Sidebar: all nav links, active states, admin submenu get dark mode
- Auth pages (login, register, forgot, reset): full dark mode
- Protected pages (dashboard, account, setup, license-keys,
  proclamations, categories): full dark mode
- Home page, error page, admin page: dark:text-gray-100

src/routes/login/+page.svelte

@@ -26,16 +26,16 @@
 </script>
 
 <Window>
-	<div>
+	<div class="dark:text-gray-100">
 		{#if verified}
 			<div
-				class="mb-4 rounded-lg border border-green-200 bg-green-50 p-4 text-green-700"
+				class="mb-4 rounded-lg border border-green-200 bg-green-50 p-4 text-green-700 dark:border-gray-700 dark:bg-gray-800 dark:text-gray-300"
 			>
 				Your email has been verified. You can now log in.
 			</div>
 		{/if}
 		{#if error}
-			<span class="text-red-600">{error}</span>
+			<span class="text-red-600 dark:text-gray-300">{error}</span>
 		{/if}
 		<form
 			onsubmit={handleSubmit}
@@ -44,13 +44,13 @@
 			<p>Login</p>
 			<input type="email" placeholder="Email Address" bind:value={email} required class="my-2" />
 			<input type="password" placeholder="Password" bind:value={password} required class="my-2" />
-			<button class="mt-4 rounded bg-blue-200 px-4 py-2" type="submit">Sign In</button>
+			<button class="mt-4 rounded bg-blue-200 px-4 py-2 dark:bg-gray-700 dark:text-gray-100" type="submit">Sign In</button>
 		</form>
 		<div class="mt-2 flex flex-col items-center gap-2">
-			<a href="/forgot-password" class="text-sm text-blue-600 hover:text-blue-800"
+			<a href="/forgot-password" class="text-sm text-blue-600 hover:text-blue-800 dark:text-gray-400 dark:hover:text-gray-200"
 				>Forgot Password?</a
 			>
-			<a href="/register" class="text-sm text-blue-600 hover:text-blue-800"
+			<a href="/register" class="text-sm text-blue-600 hover:text-blue-800 dark:text-gray-400 dark:hover:text-gray-200"
 				>Don't have an account? Register</a
 			>
 		</div>