feat(web): TrackMenuItem primitive for M7 #372

Single-entry button used by TrackMenu. Supports aria-disabled (kept
visible to preserve menu height when admin-only or pre-#352 entries
are non-functional) and a `danger` flag for the oxblood-tinted
"Remove from library" entry.

web/src/lib/components/TrackMenuItem.svelte

@@ -0,0 +1,43 @@
+<script lang="ts">
+  import type { Component } from 'svelte';
+
+  let {
+    icon,
+    label,
+    onclick,
+    disabled = false,
+    danger = false,
+    title,
+  }: {
+    /** Lucide icon component (or any Svelte component matching the Lucide signature). */
+    icon: Component<{ size?: number; strokeWidth?: number; class?: string }>;
+    label: string;
+    onclick?: () => void;
+    disabled?: boolean;
+    /** Renders in oxblood for destructive actions ("Remove from library"). */
+    danger?: boolean;
+    /** Tooltip text — used to explain disabled state ("Coming with playlists"). */
+    title?: string;
+  } = $props();
+
+  const Icon = $derived(icon);
+
+  function fire() {
+    if (disabled || !onclick) return;
+    onclick();
+  }
+</script>
+
+<button
+  type="button"
+  role="menuitem"
+  aria-disabled={disabled}
+  {title}
+  onclick={fire}
+  class="flex w-full items-center gap-2 rounded px-2 py-1.5 text-sm
+         {disabled ? 'cursor-not-allowed text-text-muted' : 'text-text-primary hover:bg-surface-hover'}
+         {danger && !disabled ? 'text-action-destructive' : ''}"
+>
+  <Icon size={14} strokeWidth={1} />
+  {label}
+</button>