fix: update DeepSeek demo adapter import

[Bortlesboat]

Summary

• update examples/demo_deepseek_analysis.py to import the existing deepseek_adapter module
• use the existing create_deepseek_llm factory instead of the missing deepseek_direct_adapter
• add a static regression test that verifies example adapter imports point at real adapter modules and exported names

Validation

• uv run --no-sync pytest tests/test_demo_deepseek_analysis_imports.py -q
• uv run --no-sync python -m py_compile examples/demo_deepseek_analysis.py tests/test_demo_deepseek_analysis_imports.py
• git diff --check

Fixes #702