[feature] Layer 1 input normalisation (NFKC + JSON normalization + decoding)

[RachanaB5]

Summary

Implements Layer 1 input normalisation for the Cognitive Firewall pipeline to ensure consistent and safe preprocessing of all incoming data before further analysis.

Features

• Unicode normalization using NFKC
• Removal of zero-width and invisible characters
• Safe percent-decoding with preservation of literal +
• Recursive JSON normalization for:
  • strings
  • arrays ([]interface{})
  • maps (map[string]interface{})
• Graceful handling of nil values

Integration

• Integrated into listener flow after HMAC and nonce validation
• Normalised payload replaces original payload before further pipeline stages

Tests

• Unit tests for normalization logic
• JSON normalization tests covering nested structures
• Listener test for invalid JSON payload handling

Validation

• Successfully built and ran the sidecar locally
• Verified service starts and listens on UDS socket (/tmp/acf.sock)
• Confirmed normalization pipeline executes without runtime errors

Notes

This establishes the foundational preprocessing layer required for downstream:

• injection detection
• risk scoring
• policy evaluation

Closes #8