17. Add optional score normalization strategy interface

[opeyemibami]

Description

VAAS scores are currently returned raw.
Some users may want normalized or calibrated scores for downstream ranking or analysis.

This issue proposes adding an optional, explicit score normalization interface.

Scope

• Optional normalization strategy (e.g. none, min-max, z-score)
• Default behavior unchanged
• Strategy must be explicit and opt-in

Acceptance Criteria

• Raw scores remain default
• Normalized scores are reproducible
• No hidden thresholding or decision logic

Notes / Constraints

• Must not imply absolute decision-making
• Must preserve relative-score philosophy

Testing Requirements

• Test raw vs normalized outputs
• Test reproducibility of normalization