Rework the changelog and release flow to remove the aspirational
top-level version that made it unclear whether new entries were
landing in an already-released section.
Schema change: `changelog.json` now has an explicit `unreleased`
object instead of hoisting the upcoming version to the top level. The
old `{version, sections, history}` layout becomes
`{unreleased, history}`, with the previously-released version moved
into `history[0]`.
New entries always go into `unreleased` via `changelog.py`. Releasing
is a single atomic operation (`release.py X.Y.Z`) that promotes
`unreleased` into `history[0]` with the target version number,
propagates the version to every source file, and regenerates the
markdown artifacts.
Script renames:
- `_changelog.py` → `changelog_lib.py` (no more underscore-prefixed
module that's imported by two siblings)
- `changelog-add.py` → `changelog.py`
- `update-version.py` → `release.py` (does more than just version
propagation — the name now reflects the full release action)
CHANGELOG.md rendering follows Keep a Changelog: a `## [Unreleased]`
block appears on top only when there are unreleased entries; the
update-json/changelog.md shown in Magisk/KSU popups still skips
Unreleased (only released versions make sense there).
Docs (docs/changelog.md, docs/releasing.md, CONTRIBUTING.md, CLAUDE.md)
updated with the new commands and the clarified model.
CLAUDE.md additionally gains a "read these before doing any work"
section that lists the contributor docs — so future sessions load the
workflow rules into context instead of skipping them as optional.
