Translate all Chinese comments, docstrings, log messages, error messages,
and LLM prompt text to English across the entire backend codebase.
Locale translation files (locales/*.json) are unchanged.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Simplifies infrastructure: ACR + Container Apps Environment only.
Log Analytics can be added later if observability is needed.
Update INSTALL.md accordingly.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>