release: prepare base-bash-libs-demo 0.1.2

Goal

Prepare the post-v0.1.1 documentation-correction patch release.

Carry the fixes from docs: show expected output and troubleshooting for the quick start #64, docs: deliver the code-level before/after that the README promises #66, and docs: move the filesystem trust boundary out of the lifecycle page and gate single-H1 docs #68.
Update stale standalone-release and cross-repository release references discovered during the review.
Keep Beacon's committed Base Bash v2.2.0 vendor pin unchanged.
Build and remotely verify the four canonical Beacon v0.1.2 assets from the final merged commit.

All three patch-scope issue fixes are merged and covered by documentation contracts or executable examples.
VERSION and CHANGELOG agree on 0.1.2.
Full validation and the required consumer/artifact aggregate pass.
The final annotated tag and four release assets bind to the merged commit.
Release URL and checksums are recorded here.

Do not change the committed framework pin or pull the v0.2.0 adoption issues (#65, #67, #69) into this patch.

Published base-bash-libs-demo v0.1.2.

Release: https://github.com/basefoundry/base-bash-libs-demo/releases/tag/v0.1.2
Source commit: ab4da09cdca638354570aee1b44a3f47a8664551
Annotated tag: v0.1.2 resolves to that commit.
Archive SHA-256: 19d0995c00744433a5480c8d430f828a3cffecf733a68ca753b49701bffd7e54
The four release assets were uploaded and downloaded again for verification.
Remote checksum verification passed for the archive, SPDX, and provenance assets.
Remote artifact verification passed.
The committed Base Bash vendor remains v2.2.0 at d8894bf4453e6b6beaa6de7ce2e082497cb236f2.

Issues #64, #66, and #68 are included. Issues #65, #67, and #69 remain planned for v0.2.0.