xchain-e2e-test v0.19.0

xchain-e2e-test v0.19.0, part of the XChain Platform v0.19.0 train.

The settle path is drilled across the hub and indexer canonicals, signing with one and
verifying with the other, and the full distribution rail is drilled from a mint through a
lock to an airdrop. Gas is funded off Bitcoin by bridging instead of issuing locally, since
a broadcast gas issue is refused off Bitcoin, and every direct gas mint is routed through a
chain-aware helper with helper ticks lifted above the namespace floor. The full bitcoin leg
of this suite on the release branch is the train's structure-pass proof: its action suites
registered at the measured baseline (273 passing, 32 pending, 0 failing). Restructured
under the platform code-structure standard (feature directories, snake_case files, split
test suites, restored comments).

Full notes in CHANGELOG.md. The platform release with every component tarball is on xchain-node:
https://github.com/XChain-Platform/xchain-node/releases/tag/v0.19.0