Design a price anomaly detector that alerts when a price deviates too far from
a reference price.

Module name: price_guard
Parameters:
  - WIDTH = 24       // Total bit width (Q15.8 fixed-point)
  - FRAC  = 8        // Fractional bits

Ports:
  - input  [WIDTH-1:0] current_price   // Current market price
  - input  [WIDTH-1:0] reference_price // Reference/fair price
  - input  [WIDTH-1:0] threshold       // Maximum allowed deviation
  - output             alert           // 1 if price deviation exceeds threshold

Functional specification:
  - Computes |current_price - reference_price| (absolute difference)
  - alert = 1 if absolute difference > threshold
  - Purely combinational
  - Treats prices as unsigned fixed-point values
