feat(renderer): full article reader with TOC, font controls & print (M10.1)

- ArticleReader.vue: sticky TOC sidebar (desktop), mobile dropdown
- Auto-generated heading anchors with IntersectionObserver tracking
- Reading time estimate, font size controls (persisted localStorage)
- Print mode opens clean window with serif typography
- Long-form detection (>800 words + headings) shows "Read as article"
- Removed isDark conditionals from ArticleDetail (dark-only app)

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

packages/app/src/components/content/ContentPanel.vue

@@ -87,6 +87,12 @@
             :article="selectedArticle"
             @back="closeArticleDetail"
           />
+          <ArticleReader
+            v-else-if="longFormArticle"
+            :content="longFormArticle.content"
+            :title="longFormArticle.title"
+            @back="closeLongFormArticle"
+          />
 
           <!-- Grid views by active tab -->
           <component
@@ -170,6 +176,7 @@ import PodcastGrid from './PodcastGrid.vue'
 import PodcastDetail from './PodcastDetail.vue'
 import NewsGrid from './NewsGrid.vue'
 import ArticleDetail from './ArticleDetail.vue'
+import ArticleReader from '@/components/renderers/ArticleReader.vue'
 import MagazineGrid from './MagazineGrid.vue'
 import ProjectGrid from './ProjectGrid.vue'
 import NostrGrid from './NostrGrid.vue'
@@ -218,11 +225,13 @@ const {
   openPodcastDetail,
   closePodcastDetail,
   closeArticleDetail,
+  longFormArticle,
+  closeLongFormArticle,
   closePanel,
 } = useContentPanel()
 
 const hasDetailOpen = computed(() =>
-  !!(selectedFilm.value || selectedBook.value || selectedTVSeries.value || selectedSong.value || selectedPodcast.value || selectedArticle.value || selectedDesignSystemItem.value)
+  !!(selectedFilm.value || selectedBook.value || selectedTVSeries.value || selectedSong.value || selectedPodcast.value || selectedArticle.value || selectedDesignSystemItem.value || longFormArticle.value)
 )
 
 const windowWidth = ref(window.innerWidth)