fix(settlement): enforce MAX_FEE_BPS ceiling independent of governance config (#521)

[Hollujay]

Closes #521

Problem

bettapay_common::constants::MAX_FEE_BPS = 5_000 (50%) was documented as intended for settlement adoption, but settlement's setters only checked against BPS_DENOMINATOR (10_000 / 100%):

if rule.platform_fee_bps > BPS_DENOMINATOR || rule.network_fee_bps > BPS_DENOMINATOR {
    panic_with_error!(env, SettlementError::InvalidFeeBps);
}

The tighter 50% ceiling was only ever enforced by validate_fee_against_governance, which calls into the governance contract's get_fee_config and is a no-op when governance hasn't configured a FeeConfig yet:

if fee_config.is_void() {
    return; // no ceiling to enforce
}

So before governance is configured, set_settlement_rule / set_default_rule would accept a per-fee value up to 100% — twice the intended 50% ceiling — and the two contracts enforced inconsistent fee ceilings.

Fix

Added an explicit MAX_FEE_BPS check alongside the existing MIN_FEE_BPS/BPS_DENOMINATOR checks in:

• settlement_contract/src/settlement.rs — the public set_settlement_rule and set_default_rule entry points.
• settlement_contract/src/admin.rs — the internal _set_settlement_rule / _set_default_rule used by the scheduled-operation execution path (these had the same gap and no governance validation at all).

Both now reject any per-fee value above MAX_FEE_BPS, independent of whether a governance FeeConfig exists. validate_fee_against_governance still tightens the ceiling further once governance does configure one — it's a floor for the ceiling, not the source of it.

Also updated the MAX_FEE_BPS and SettlementError::InvalidFeeBps doc comments, which previously described the pre-fix behavior.

Test plan

• Added to settlement_contract/src/tests/admin_tests.rs:
  • set_settlement_rule_rejects_platform_fee_above_max_fee_bps
  • set_settlement_rule_rejects_network_fee_above_max_fee_bps
  • set_settlement_rule_accepts_fee_at_max_fee_bps_ceiling (5000 bps still valid)
  • set_default_rule_rejects_fee_above_max_fee_bps
• cargo test --workspace passes (33 governance + 20 settlement tests)
• cargo build --workspace --target wasm32-unknown-unknown --release succeeds for both contracts

[therealjhay]

Kindly fix the merge conflicts in this pull request.

[Hollujay]

Ci failure fixed @therealjhay