fix(app): harden persistence, player performance, content extraction

- Fix chat persistence: unwrap Vue Proxy objects before IDB storage,
  flush pending saves on page unload/visibility change, use immediate
  saves for conversation creation and seed migration
- Fix player performance: parallel music search across providers,
  server-side LRU cache, client-side result cache, audio element reuse,
  instant UI feedback, abort stale searches, next-song prefetch
- Fix content extraction: strip recipe/event tags in stripContentTags,
  extend cleanMagazineContent regex for all _ext patterns
- Fix PlayerBar: move to App.vue root to avoid stacking context clipping,
  remove unused isDark conditionals (dark-only app)
- Add /seed command: loads 15 seed conversations from fixture index,
  opens history panel, switches to first seed conversation
- Add seed prompt index: 15 realistic AI prompt/response pairs covering
  films, songs, books, TV, places, podcasts, code, images, recipes, events
- Add seedExtraction.test.ts: 60 tests validating extraction counts,
  tag stripping completeness, and data integrity

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

packages/app/scripts/generate-seed-chats.ts

@@ -0,0 +1,21 @@
+/**
+ * Generate .dev/chats.json from the seed prompt index.
+ * Run: npx tsx packages/app/scripts/generate-seed-chats.ts
+ */
+import { seedPromptsToConversations } from '../src/__tests__/fixtures/seedPrompts'
+import { writeFileSync, mkdirSync, existsSync } from 'fs'
+import { resolve, dirname } from 'path'
+
+const outPath = resolve(dirname(new URL(import.meta.url).pathname), '../.dev/chats.json')
+const dir = dirname(outPath)
+if (!existsSync(dir)) mkdirSync(dir, { recursive: true })
+
+const conversations = seedPromptsToConversations()
+const ids = Object.keys(conversations)
+const data = {
+  conversations,
+  activeConversationId: ids[0] ?? null,
+}
+
+writeFileSync(outPath, JSON.stringify(data, null, 2), 'utf-8')
+console.log(`Wrote ${ids.length} seed conversations to ${outPath}`)