refactor: move llm-playground from services/ to apps/playground/

The LLM playground is a SvelteKit web app (frontend), not a backend
microservice. Moving it to apps/ follows the monorepo convention where
all user-facing apps live under apps/.

- Moved services/llm-playground/ → apps/playground/apps/web/
- Renamed package from @mana-llm/playground to @playground/web
- Updated Dockerfile paths for new location
- Updated docker-compose.macmini.yml build context
- Removed unused concurrently dependency
- Added parent package.json

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/playground/package.json

@@ -0,0 +1,7 @@
+{
+	"name": "playground",
+	"private": true,
+	"scripts": {
+		"dev": "turbo run dev"
+	}
+}