Add XAUt to Aave v3 Core Instance

The proposal follows Aave's standard governance payload pattern: the on-chain action is a single execute() call (delegatecall/fallback) to a pre-deployed payload contract. This contract's internal logic (verified via the linked GitHub implementation and test files) is expected to contain the exact listing parameters described in the prose (isolation mode, caps, LTV/LT, rate curve, oracle assignment, emission admin). Because the decoded calldata exposes no arguments beyond the target address and function selector, it is not possible to directly verify each numeric parameter (LTV, caps, debt ceiling, rate curve, etc.) or the oracle/emission-admin addresses against the calldata itself — this is inherent to how Aave's on-chain payload execution works and not a sign of misrepresentation. There is no evidence of a target mismatch, omitted action, or extra claim: the single action target is consistent with a listing payload, and the description's claims (new reserve listing, oracle assignment, emission admin) are all things such a payload contract typically performs. Given the opacity of the calldata (no decoded parameters to cross-check), confidence in this assessment is necessarily low, but no discrepancy is apparent from what is available, so the overall assessment defaults to consistent rather than flagging a false alarm.