fix: upgrade python-multipart to fix ReDoS vulnerability (CVE-2024-47874)

[JNK234]

Problem

root/requirements.txt pins python-multipart==0.0.9 which has a known high-severity ReDoS vulnerability (CVE-2024-47874) in Content-Type header parsing. This is a direct FastAPI dependency for file upload handling.

Fix

Upgrade to python-multipart>=0.0.12.

Files to Change

• root/requirements.txt

Acceptance Criteria

• python-multipart upgraded to 0.0.12+
• File uploads still work correctly
• No other dependency conflicts