feat: add element_access_denied.svelte; use in badge review page

- New reusable element_access_denied.svelte with title, message, action props
- Badge review page: swap inline 'Access Denied' card with the component
- Project doc: all 6 steps complete, status → Complete

src/lib/elements/element_access_denied.svelte

@@ -0,0 +1,34 @@
+<script lang="ts">
+    import { ShieldX } from '@lucide/svelte';
+
+    interface Props {
+        title?: string;
+        message?: string;
+        action_label?: string;
+        on_action?: () => void;
+    }
+
+    let {
+        title = 'Access Denied',
+        message = 'You do not have permission to view this content.',
+        action_label = '',
+        on_action = undefined
+    }: Props = $props();
+</script>
+
+<div class="card p-6 space-y-4 max-w-sm">
+    <div class="flex items-center gap-2 text-error-500">
+        <ShieldX size="1.2em" />
+        <h3 class="text-lg font-semibold">{title}</h3>
+    </div>
+    <p class="text-sm text-gray-700">{message}</p>
+    {#if action_label && on_action}
+        <button
+            type="button"
+            class="btn preset-tonal-surface w-full"
+            onclick={on_action}
+        >
+            {action_label}
+        </button>
+    {/if}
+</div>