fix(data): integer overflow vulnerabilities in money parsing

[cpcloud]

Summary

Code audit revealed critical integer overflow vulnerabilities in money parsing and formatting functions.

Issues Fixed

1. Integer Overflow in parseCents (CRITICAL)

• Impact: Silent data corruption when parsing very large dollar amounts
• Root cause: Multiplication by 100 without overflow check
• Fix: Added bounds check to reject values > $92,233,720,368,547,758

2. math.MinInt64 Negation Overflow (HIGH)

• Impact: Potential panic when formatting the most negative int64 value
• Root cause: -math.MinInt64 overflows because abs(MinInt64) > MaxInt64
• Fix: Special case handling treats MinInt64 as MaxInt64 for display

Testing

Added comprehensive edge case tests:

• Overflow rejection validation
• Max safe value acceptance
• MinInt64 formatting without panic

All tests pass. Full audit documented in CODE_REVIEW_FINDINGS.md.