Public source snapshots for extended-public-key scope, release20261017-v1.

Core source files are unchanged snapshots of tagv0.21.5.8, resolved commit
ec1b6489a900d09cf5991e220dce089c77a232a2, under the supplied MIT license.
BIP32 excerpt is edited and clearly labeled. It retains the original author,
license notice, specified line ranges, full upstream hash and public vector1
master, m/0 hardened and m/0 hardened/1 public extended keys only. The full upstream test-vector seeds and
extended private keys are omitted. BSD-2-Clause terms are included.
BIP44 and SLIP44 are represented by a short authored factual mapping plus exact
source links and upstream hashes; full upstream files are not redistributed.

These are implementation/specification sources. Their presence does not prove
an experiment ran, establish the real derivation layout of a user's wallet,
promise all-wallet compatibility or prove funds/ownership/complete history.
The experiment independently documents its own inputs, outputs and limitations.
Standard public test fixtures are not wallets to fund. No user private material
was accessed. No node or wallet operation is performed by this source package.
