Releases v0.42.1

[johnnyt]

Release prep for statifier_blocks 0.42.1, a documentation-only patch. Refs: sb-pqnx.

The conductor merges this and tags the merged commit v0.42.1; the tag push publishes through .github/workflows/release.yml. This PR does not tag or publish.

What the commit does

• mix.exs: @version 0.42.0 -> 0.42.1.
• lib/statifier_blocks/compiler.ex: @compiler_version 0.42.0 -> 0.42.1 (release extension, Step A; compiler_test.exs's "compiler_version is this package's version" asserts the two agree).
• CHANGELOG.md: a new ## [0.42.1] 2026-10-05 section above 0.42.0's, in the file's existing heading form and dated with the local date, and [0.42.1]: https://github.com/riddler/statifier_blocks/releases/tag/v0.42.1 at the top of the link-reference block.
• README.md: not touched. A patch leaves the exact-minor install pin at ~> 0.42.0, which already admits 0.42.1 (release extension, "The README install pin").

No changelog.d/ fragment is promoted or deleted: none is on main (the directory holds only its README.md).

The hand-written section

The release extension's Step B promotes fragments, and documentation takes no fragment in this repository (changelog.d/README.md, "Do not write a fragment for: ... documentation"). So the section's bullets are written here rather than carried over, ruled by the operator, 2026-10-05. They name what changed for a reader of the published docs since v0.42.0:

• the hexdocs sidebar grouping (groups_for_extras in mix.exs): the guide to describing a document under How-to guides, the README and the CHANGELOG ungrouped at the top;
• the "How to" titles of the flow patterns, profiles and theming guides (no file renamed);
• the Note section's place in StatifierBlocks.Editor.Inspector's module documentation.

Why a patch

git log v0.42.0..origin/main lists the changes this release carries. Outside docs, ADRs, tests, CI and agent tooling they are: two code comments (describe.ex, the Map hook's JavaScript), the editor's note read going through its existing private block lookup, the inspector's moduledoc text, and the groups_for_extras docs config. None adds or removes an event, reason, option or enum member a host matches on, so the release is a patch. No runtime dependency is added and mix.lock is untouched.

Gate

Full mix quality green on the committed tree: 3,954 of 3,954 tests, 95.3% coverage, dialyzer clean, ADR cites green, docs without warnings. mix hex.build builds statifier_blocks 0.42.1.