- Reorganize sidebar into sections with headers (main items, Settings)
- Rename "API Keys" to "AI Provider Keys" with clear description
- Rename "TPMJS API Keys" to "Platform API Keys"
- Add info banners explaining the difference:
- AI Provider Keys: credentials for OpenAI, Anthropic, etc.
- Platform API Keys: authentication for TPMJS platform (tpmjs_sk_...)
- Update empty states with clearer messaging
- Use distinct icons (puzzle for AI providers, key for platform)