feat(renderer): PDF viewer with page nav & zoom controls (M10.2)

- PdfViewer.vue: lazy-loads pdfjs-dist, renders to canvas
- Page navigation (arrows), zoom controls (50%–200%)
- Keyboard navigation (arrow keys)
- Integrated into content panel via openPdfViewer()

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

packages/app/src/composables/useContentPanel.ts

@@ -51,6 +51,7 @@ const activeTab = ref<ContentTab>('film')
 const availableTabs = ref<ContentTab[]>([])
 const selectedDesignSystemItem = ref<DesignSystemItem | null>(null)
 const longFormArticle = ref<{ content: string; title?: string } | null>(null)
+const pdfUrl = ref<{ url: string; title?: string } | null>(null)
 
 export interface DesignSystemItem {
   id: string
@@ -273,6 +274,7 @@ export function useContentPanel() {
     selectedMagazineSection.value = null
     selectedDesignSystemItem.value = null
     longFormArticle.value = null
+    pdfUrl.value = null
   }
 
   function openFilmDetail(film: Film) { clearAllSelections(); selectedFilm.value = film }
@@ -296,6 +298,9 @@ export function useContentPanel() {
   function openLongFormArticle(content: string, title?: string) { clearAllSelections(); longFormArticle.value = { content, title }; panelOpen.value = true }
   function closeLongFormArticle() { longFormArticle.value = null }
 
+  function openPdfViewer(url: string, title?: string) { clearAllSelections(); pdfUrl.value = { url, title }; panelOpen.value = true }
+  function closePdfViewer() { pdfUrl.value = null }
+
   function openMagazineSectionDetail(section: MagazineSection, index: number) {
     clearAllSelections()
     selectedMagazineSection.value = section
@@ -443,6 +448,9 @@ export function useContentPanel() {
     longFormArticle,
     openLongFormArticle,
     closeLongFormArticle,
+    pdfUrl,
+    openPdfViewer,
+    closePdfViewer,
     enterDesignSystemMode,
     closePanel,
     showAllFilms,