Combine Rules and Admin corner links into one upper-right menu

Replace the fixed Rules link (upper-left) and the creator-only Admin
link (upper-right) with a single collapsible ☰ Menu in the upper right,
leaving the event log alone in its corner. CornerMenu always lists the
Rules link; pages can contribute context-specific entries through the
extraMenuLinks store, which Dashboard uses for the creator-only Admin
link. This gives future misc sub-pages a home without eating more
screen corners.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/components/CornerMenu.svelte

@@ -0,0 +1,87 @@
+<script>
+    import { extraMenuLinks } from '../lib/menu';
+
+    let open = false;
+
+    const baseLinks = [
+        { label: '📖 Rules', href: '/rules', external: true, title: 'Open the rulebook in a new tab' },
+    ];
+
+    $: links = [...$extraMenuLinks, ...baseLinks];
+
+    function handleWindowClick(event) {
+        if (open && !event.target.closest('.corner-menu')) {
+            open = false;
+        }
+    }
+</script>
+
+<svelte:window on:click={handleWindowClick} />
+
+<div class="corner-menu">
+    <button class="menu-toggle" class:open on:click={() => (open = !open)} title="Menu">
+        ☰ Menu
+    </button>
+    {#if open}
+        <nav class="menu-dropdown">
+            {#each links as link}
+                <a
+                    href={link.href}
+                    target={link.external ? '_blank' : undefined}
+                    rel={link.external ? 'noopener' : undefined}
+                    title={link.title}
+                    on:click={() => (open = false)}
+                >{link.label}</a>
+            {/each}
+        </nav>
+    {/if}
+</div>
+
+<style>
+    .corner-menu {
+        position: fixed;
+        top: 12px;
+        right: 16px;
+        z-index: 1001;
+        text-align: right;
+    }
+    .menu-toggle {
+        padding: 6px 14px;
+        border-radius: 16px;
+        background: rgba(10, 15, 25, 0.9);
+        border: 1px solid var(--glass-border-focus);
+        color: var(--neon-cyan);
+        font-size: 0.85rem;
+        font-weight: 700;
+        font-family: var(--font-heading);
+        cursor: pointer;
+    }
+    .menu-toggle:hover, .menu-toggle.open {
+        background: rgba(0, 242, 254, 0.1);
+    }
+    .menu-dropdown {
+        margin-top: 6px;
+        display: flex;
+        flex-direction: column;
+        background: rgba(10, 15, 25, 0.95);
+        border: 1px solid var(--glass-border-focus);
+        border-radius: 12px;
+        overflow: hidden;
+    }
+    .menu-dropdown a {
+        padding: 8px 16px;
+        color: var(--neon-cyan);
+        font-size: 0.85rem;
+        font-weight: 700;
+        text-decoration: none;
+        font-family: var(--font-heading);
+        text-align: right;
+        white-space: nowrap;
+    }
+    .menu-dropdown a:hover {
+        background: rgba(0, 242, 254, 0.1);
+    }
+    .menu-dropdown a + a {
+        border-top: 1px solid rgba(0, 242, 254, 0.15);
+    }
+</style>