[FEATURE] Add input validation per IEEE 1584-2018 Section 4.2

[sramharack]

Feature Description

Validate inputs against IEEE 1584-2018 model validity ranges before calculation.

Validation Rules (Section 4.2)

Parameter	LV (≤600V)	MV (>600V)
Voltage	208V - 600V	601V - 15,000V
Current	500A - 106,000A	200A - 65,000A
Gap	6.35mm - 76.2mm	19.05mm - 254mm
Distance	≥ 305mm	≥ 305mm

Proposed Implementation

def validate_inputs(ibf_ka, voc_kv, gap_mm, distance_mm) -> List[str]:
    """Return list of validation errors, empty if valid."""
    errors = []
    if voc_kv < 0.208 or voc_kv > 15.0:
        errors.append(f"Voltage {voc_kv} kV outside valid range 0.208-15 kV")
    # ... etc
    return errors

Acceptance Criteria

• Validation function created
• Clear error messages with valid ranges
• Integrated into calculate_arc_flash()
• Option to warn vs raise error
• Unit tests for boundary conditions