add ARB to Aave V3 Arbitrum Pool

The proposal follows Aave's standard cross-chain governance pattern: the only decoded on-chain action is a generic execute(address) call that forwards execution to a payload contract deployed on Arbitrum (referenced in the proposal's 'Implementation' link). This is boilerplate for Aave AIPs that configure L2 markets — the mainnet transaction itself never contains the granular risk parameters (supply cap, LTV, interest rate curve, etc.) described in the prose, because those are encoded inside the target payload contract's own logic, which is not present in the decoded calldata provided here. Because we only have this single opaque execute() call and not the decoded internals of the Arbitrum payload, we cannot directly verify or refute the specific numeric risk parameters (LTV 50%, LT 60%, caps, etc.) claimed in the description. Nothing in the visible calldata contradicts the description, and the pattern (execute→payload) is exactly what one would expect for this type of proposal, so there is no evidence of a discrepancy. However, confidence is low because the actual listing parameters are not independently verifiable from the calldata shown — a full audit would need the decoded internals of the target payload contract to confirm parameter-level accuracy from the on-chain configuration.