7.1 Add runtime invariant checks in development mode

[Masked-Kunsiquat]

Priority: Low
Estimated Time: 2 hours
Milestone: Optional Enhancements

Problem

Mathematical invariants (conservation laws) only verified in tests, not runtime.

Tasks

• Add invariant checks to calculateBalances()
• Add invariant checks to normalizeShares()
• Only run in development mode
• Log warnings instead of throwing in production

Success Criteria

• Invariants checked in development
• No performance impact in production
• Helpful error messages

See REFACTOR_ROADMAP.md for implementation.