H4: add internal_api_base_url setting to config.py (default http://localhost:8888,
env-overridable via INTERNAL_API_BASE_URL); replace all 5 hardcoded base_url
strings in chat_service.py.
H6: add post-read size check in both Excel and STEP upload handlers;
raises HTTP 413 when content exceeds settings.max_upload_size_mb.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
HartmutandClaude Sonnet 4.6