Add logging middleware for prediction requests

[Alvi24-hub]

No logging exists. Need to track requests for debugging and monitoring.

• Log timestamp, text preview (first 50 chars), and prediction
• Use Python's logging module
• Configurable log level via .env

[Alvi24-hub]

@Userunknown84 pls assign this to me under SSoC2026

[shashankashekharnayak2006-stack]

@Alvi24-hub you are assinged

[Alvi24-hub]

@shashankashekharnayak2006-stack pls add the SSoc label to this