fix/issue-409-406-363-403-economics-governance-security

[devchant]

Summary

This PR strengthens Xelma’s economic correctness, governance controls, and security observability across settlement, treasury, parameter management, and guard handling.

Changes

• Aligned simulate_payout with live settlement logic across UpDown, Precision, and fee models to prevent calculation drift.
• Added differential and property-based coverage using randomized pots to verify payout parity and economic invariants.
• Hardened protocol fee treasury withdrawals to enforce balance conservation, prevent over-withdrawal and double-withdrawal, and emit withdrawal events.
• Added an on-chain parameter constitution with immutable, timelocked, and dual-approval parameter classes, including amendment proposals, timelocks, veto windows, atomic activation, and audit events.
• Standardized action_rejected events across authorization, pause, timing-window, oracle, and other guard failures.
• Added supporting governance, treasury, settlement, and event-coverage tests and documentation.

Validation

• Differential and property-based settlement tests
• Treasury conservation and withdrawal safety tests
• Governance amendment, timelock, veto, and activation tests
• Guard-failure event coverage tests
• Documentation and audit-event verification

Related Issues

Closes #409
Closes #406
Closes #363
Closes #403