Protect AI and tracing routes with API key

[MaxGhenis]

Summary

• extend the shared API-key guard to the AI prompt and tracer-analysis routes in addition to simulation-analysis
• add focused route tests for unauthorized and authorized access to the protected AI routes
• add a changelog fragment for the new protection

Testing

• FLASK_DEBUG=1 uv run --python 3.11 pytest tests/unit/routes/test_ai_route_auth.py tests/unit/routes/test_simulation_analysis_auth.py -q

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.48%. Comparing base (ddd65d8) to head (5c91913).
⚠️ Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3399      +/-   ##
==========================================
+ Coverage   72.58%   73.48%   +0.90%     
==========================================
  Files          56       57       +1     
  Lines        2477     2614     +137     
  Branches      431      466      +35     
==========================================
+ Hits         1798     1921     +123     
- Misses        598      608      +10     
- Partials       81       85       +4     

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