refactor(app): consolidate seeds into single conversation

All 15 seed prompts now load as one conversation ("Content Showcase")
instead of 15 separate ones. /seed collapses chat to show PromptIndex
so users can quickly pick any prompt to see its content surface.

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

packages/app/src/components/chat/ChatWindow.vue

@@ -332,12 +332,10 @@ async function handleSend(text: string, images: ImageAttachment[] = []) {
 
   if (trimmed === '/seed') {
     await chatStore.loadSeedChats()
-    // Switch to first seed conversation and open history
-    const firstSeed = chatStore.conversationList.find(c => c.id.startsWith('seed-'))
-    if (firstSeed) {
-      chatStore.setActiveConversation(firstSeed.id)
-    }
-    chatStore.showHistory = true
+    // loadSeedChats already switches to the seed conversation
+    // Collapse chat so user sees PromptIndex for quick picking
+    chatStore.chatCollapsed = true
+    chatStore.showHistory = false
     return
   }