fix: F-2026-18825 | [Dual Defense] One Invalid Gateway Sibling Erases Valid Outbounds After Committed UEA Burn (#323)

* fix: attach payload outbounds inside ExecutePayloadV2's cache (F-2026-18825)

The gateway burn was committed before the handlers attached the outbounds, so
one invalid leg of a multicall erased the valid ones with their burns already
final and the failure swallowed into RevertError.

* test: cover UEA multicall outbound atomicity (F-2026-18825)

Author: 0xNilesh