feat(app): add always-visible Prompt tab with magazine brief style

Adds a 'Prompt' tab that is always present as the rightmost tab in the
content panel. Shows the user's original query as a single magazine-style
tile using the existing MagazineGrid component.

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

packages/app/src/composables/useContentPanel.ts

@@ -139,8 +139,10 @@ export function useContentPanel() {
     }
 
     const tabs = filterTabsByContext(userQuery, films.length > 0, songs.length > 0, podcasts.length > 0, books.length > 0, tvSeries.length > 0, images.length > 0, places.length > 0, hasNews, hasWebsites, hasMagazine, hasNostr, hasApps, hasCode)
-    availableTabs.value = tabs.length > 0 ? tabs : ['film']
-    activeTab.value = tabs[0] ?? 'film'
+    // Always append Prompt tab as the rightmost tab
+    const tabsWithPrompt = tabs.length > 0 ? [...tabs, 'prompt' as const] : ['prompt' as const]
+    availableTabs.value = tabsWithPrompt
+    activeTab.value = tabs[0] ?? 'prompt'
 
     const showFilms = tabs.includes('film')
     const showBooks = tabs.includes('book')