Implement login; add model import/export; enable enter-to-send message

[lxchinesszz]

Implement login;

docker run -d -p 3000:3000 \
  -e AI_PROVIDER=openai \
  -e AI_MODEL=kimi-k2-turbo-preview \
  -e ACCESS_CODE_LIST=123456,123213 \
  -e OPENAI_API_KEY=sk-rWCDKoOJxxxxxxxBOGZciLkXwOhmT \
  -e OPENAI_BASE_URL=https://api.moonshot.cn/v1 \
  next-ai-draw-io:latest

add model import/export;

支持中，英，日三种语言

enable enter-to-send message

issue #420

[DayuanJiang]

Thanks for the contribution! This PR bundles multiple features - could you split it into separate PRs?

1. Login feature - The project already has an access code mechanism. What's the use case for a separate login page?
2. Model import/export
3. Enter-to-send toggle - Good idea, but it would fit better in the settings panel rather than the chat input area

Also please remove the .idea/ folder.