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/scripts/generate-seed-chats.ts

@@ -1,8 +1,8 @@
 /**
  * Generate .dev/chats.json from the seed prompt index.
- * Run: npx tsx packages/app/scripts/generate-seed-chats.ts
+ * Run: pnpm -C packages/app exec tsx scripts/generate-seed-chats.ts
  */
-import { seedPromptsToConversations } from '../src/__tests__/fixtures/seedPrompts'
+import { seedPromptsToConversation } from '../src/__tests__/fixtures/seedPrompts'
 import { writeFileSync, mkdirSync, existsSync } from 'fs'
 import { resolve, dirname } from 'path'
 
@@ -10,12 +10,11 @@ const outPath = resolve(dirname(new URL(import.meta.url).pathname), '../.dev/cha
 const dir = dirname(outPath)
 if (!existsSync(dir)) mkdirSync(dir, { recursive: true })
 
-const conversations = seedPromptsToConversations()
-const ids = Object.keys(conversations)
+const conv = seedPromptsToConversation()
 const data = {
-  conversations,
-  activeConversationId: ids[0] ?? null,
+  conversations: { [conv.id]: conv },
+  activeConversationId: conv.id,
 }
 
 writeFileSync(outPath, JSON.stringify(data, null, 2), 'utf-8')
-console.log(`Wrote ${ids.length} seed conversations to ${outPath}`)
+console.log(`Wrote seed conversation (${conv.messages.length / 2} prompts) to ${outPath}`)