fix(R-W-03): reject stablePercent > multiplier^2 at commission config time

[sh3ifu]

R-W-03 — Commission config can accept fee shapes that brick the route

Problem

CommissionManager.setGlobalDefaults and setCommissionRule validated
stablePercent and multiplier only individually. The fee formula
stableFee = amount * stablePercent / multiplier^2 means that when
stablePercent > multiplier^2 the quoted fee exceeds the bridged amount,
netAmount = amount - fee underflows with Panic(0x11), and every subsequent
fundsIn/fundsOut on that route reverts until the federation fixes the config
through the timelock. Example brick config: (stablePercent = 9000, multiplier = 1).

Fix

Enforce the joint invariant stablePercent <= multiplier^2 at both setters,
reverting InvalidFeeShape(stablePercent, multiplier) otherwise.
stablePercent == multiplier^2 (100% fee, netAmount = 0) is intentionally
still allowed — it does not underflow.