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/layout.css

@@ -76,8 +76,9 @@
 
 /* ------------------------------------------------------------------ */
 /*  Dark mode — invert the gray scale                                  */
+/*  Use :root.dark so specificity matches Tailwind's :root, :host       */
 /* ------------------------------------------------------------------ */
-.dark {
+:root.dark {
   --color-gray-50: #030712;
   --color-gray-100: #111827;
   --color-gray-200: #1f2937;
@@ -90,6 +91,17 @@
   --color-gray-900: #f9fafb;
 }
 
+/* ------------------------------------------------------------------ */
+/*  Dark mode form elements                                            */
+/* ------------------------------------------------------------------ */
+:root.dark input,
+:root.dark select,
+:root.dark textarea {
+  background-color: #1f2937;
+  color: #f9fafb;
+  border-color: #374151;
+}
+
 /* ------------------------------------------------------------------ */
 /*  Force-disable transitions, animations, and remaining decoration    */
 /* ------------------------------------------------------------------ */