Improve error message when DEEPSEEK_API_KEY is not set

[withAIx]

What

Replace the current generic ValueError("DEEPSEEK_API_KEY 未设置...") with a more helpful message that guides the user to the solution.

Current Behavior

When the API key is missing, the user sees:

ValueError: DeepSeek API Key 未设置。请设置环境变量 DEEPSEEK_API_KEY 或传入 api_key 参数

Desired Behavior

The error message should include:

1. A link to the .env.example file for reference
2. A copy-pasteable export command
3. A link to the DeepSeek API key page

Example:

DeepSeek API Key not found.

To fix this:
  1. Copy .env.example to .env: cp .env.example .env
  2. Add your key to .env: DEEPSEEK_API_KEY=sk-your-key-here
  3. Or export it: export DEEPSEEK_API_KEY=sk-your-key-here

Get a key at: https://platform.deepseek.com/api_keys

Where

• src/agents/_base.py — BaseAgent.client property
• project-orchestrator/worker.py — _get_client() function
• project-orchestrator/orchestrator.py — _get_client() function