feat(app): add bookmarks/favorites with IndexedDB persistence

Create favorites Pinia store with IndexedDB backend for persistent
favorites. Add FavoriteButton.vue heart toggle (accent-colored when
active). Create FavoritesGrid.vue with type filtering. Wire favorite
buttons into FilmCard and SongCard. Add Favorites tab to ContentPanel
that appears when items are saved.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/app/src/components/ui/FavoriteButton.vue

@@ -0,0 +1,41 @@
+<template>
+  <button
+    class="p-1 rounded-full transition-all duration-200 active:scale-125"
+    :class="favorited
+      ? 'text-accent hover:text-accent/80'
+      : isDark
+        ? 'text-white/20 hover:text-white/50'
+        : 'text-gray-300 hover:text-gray-500'"
+    :aria-label="favorited ? 'Remove from favorites' : 'Add to favorites'"
+    @click.stop="$emit('toggle')"
+  >
+    <svg
+      class="w-4 h-4 transition-transform duration-200"
+      :class="{ 'scale-110': favorited }"
+      :fill="favorited ? 'currentColor' : 'none'"
+      stroke="currentColor"
+      viewBox="0 0 24 24"
+    >
+      <path
+        stroke-linecap="round"
+        stroke-linejoin="round"
+        stroke-width="2"
+        d="M4.318 6.318a4.5 4.5 0 000 6.364L12 20.364l7.682-7.682a4.5 4.5 0 00-6.364-6.364L12 7.636l-1.318-1.318a4.5 4.5 0 00-6.364 0z"
+      />
+    </svg>
+  </button>
+</template>
+
+<script setup lang="ts">
+import { useTheme } from '@/composables/useTheme'
+
+defineProps<{
+  favorited: boolean
+}>()
+
+defineEmits<{
+  toggle: []
+}>()
+
+const { isDark } = useTheme()
+</script>