feat: add Astraflow provider support

[ucloudnb666]

Summary

Adds Astraflow (by UCloud / 优刻得) as an optional OpenAI-compatible LLM provider to both the second-brain-online and second-brain-offline apps.

Astraflow is an OpenAI-compatible AI model aggregation platform supporting 200+ models. Because it is API-compatible, the integration only requires setting base_url + api_key — no new SDK or subpackage is needed.

Changes

second-brain-online

• config.py — adds ASTRAFLOW_API_KEY, ASTRAFLOW_CN_API_KEY, and USE_ASTRAFLOW settings
• application/agents/agents.py — routes LiteLLMModel to the Astraflow global endpoint when USE_ASTRAFLOW=True
• application/agents/tools/summarizer.py — routes OpenAISummarizerTool to the Astraflow global endpoint when USE_ASTRAFLOW=True
• .env.example — documents the new env vars

second-brain-offline

• config.py — adds ASTRAFLOW_API_KEY and ASTRAFLOW_CN_API_KEY settings
• .env.example — documents the new env vars

Usage

Set the following in your .env file to use Astraflow:

USE_ASTRAFLOW=True
ASTRAFLOW_API_KEY=your-key-here

The agent and summarizer will then route all requests to https://api-us-ca.umodelverse.ai/v1 instead of OpenAI.

• Global sign-up: https://astraflow.ucloud-global.com
• China sign-up: https://astraflow.ucloud.cn