feat: add save feedback prompts, featured agent fields, dynamic Dify API config, and chat improvements

- Add success/error feedback messages near submit buttons in all admin forms
- Display success prompt for 1s before redirect after save
- Show API error details on save failure
- Add isFeatured/featuredOrder fields to Agent model and admin UI
- Add difyApiUrl/difyApiKey fields for per-agent Dify API configuration
- Show featured badge column in agent admin list
- Display featured agents on homepage sorted by order
- Refactor chat page streaming with AbortController and stable userId
- Improve Dify API proxy to use per-agent credentials

package.json

@@ -21,6 +21,9 @@
     "react-markdown": "^10.1.0",
     "remark-gfm": "^4.0.1"
   },
+  "prisma": {
+    "seed": "tsx prisma/seed.ts"
+  },
   "devDependencies": {
     "@tailwindcss/postcss": "^4.0.0",
     "@types/node": "^22.13.1",