feat(contracts): treasury epoch limits, min shares, rebalance order, loss CB

[success-OG]

closes #642
closes #644
closes #645
closes #646

Summary

Adds four on-chain safety controls to the YieldVault Soroban contract:

1. Treasury withdrawal rate limiter (epoch windows) — Configurable epoch length and per-epoch cap; withdraw_treasury enforces budget, rolls windows by ledger time, and emits trswdcap / trswdep / trswd events.
2. Minimum share supply guard — set_min_share_supply blocks withdrawals that would leave 0 < total_shares < min (dust lockup prevention).
3. Deterministic strategy rebalance ordering — rebalance_strategies sorts targets by strategy address, divests in reverse order, then invests in ascending order to avoid nondeterministic drift.
4. Circuit-breaker thresholds for abnormal loss — Baseline + threshold (bps); eval_cb_loss trips on excessive drawdown, blocks sensitive ops via CircuitBreakerTripped, with admin set_cb_loss_baseline / reset_cb_loss.

Tasks closed

Task	Implementation
Treasury epoch rate limit	set_treasury_withdraw_epoch_cap, set_trs_wd_epoch_len, withdraw_treasury, TreasuryWithdrawEpochWindow
Min share supply	set_min_share_supply, check in do_withdraw
Deterministic rebalance	rebalance_strategies + sort_strategy_targets
Loss circuit breaker	set_cb_loss_thresh, set_cb_loss_baseline, eval_cb_loss, is_cb_loss_tripped, reset_cb_loss

Test plan

• cargo build in contracts/vault
• Configure treasury epoch cap/duration; verify cap rejection and window reset across epochs
• Set min_share_supply; confirm partial withdraw that leaves dust reverts with MinShareSupplyViolated
• Call rebalance_strategies with two strategies; confirm execution order is address-sorted
• Set baseline + threshold; drop total_assets; confirm CircuitBreakerTripped blocks deposit/withdraw

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