Fix Python security vulnerabilities in uv.lock

Update langchain-core 1.2.11 -> 1.2.28 (CVE-2026-34070 High)
Update Streamlit 1.52.2 -> 1.56.0 (CVE-2026-33682 Moderate)
Update requests 2.32.5 -> 2.33.1 (CVE-2026-25645 Moderate)
Update aiohttp 3.13.3 -> 3.13.5 (CVE-2026-34513 thru CVE-2026-34519 Low)
Update Pygments 2.19.2 -> 2.20.0 (CVE-2026-4539 Low)

Author: petercrocker