M3 — Cut 1.0.0

Tracking issue for milestone **M3** of the git-worktree-poi bootstrap. Context: alunduil/alunduil-infrastructure#116.

## Goal

Cut 1.0.0 once M1 and M2 are stable, so the chezmoi consumer has a pinned release to install.

## Scope (this repo)

- Version bump to `1.0.0` and a CHANGELOG release section (Keep a Changelog 1.1.0).
- Tag `v1.0.0`; the release workflow publishes linux-x86_64 and linux-aarch64 tarballs plus sha256.
- README documents the CLI surface the sweeper and the systemd unit pin against: invocation, `NAME` targeting, `--force`, exit codes.

## Out of scope

The chezmoi-side swap — `script/install/git-worktree-poi`, removing `dot_local/bin/executable_git-worktree-poi`, repointing `git-worktree-poi.service` `ExecStart`, deleting `test/git_worktree_poi.bats` — is tracked in alunduil/alunduil-chezmoi#295, which is blocked by this issue. The consumer changes live in the repo that owns those files rather than being described twice.

## Exit

`v1.0.0` released; both platform artifacts download and verify; the CLI surface is documented.

## Open question (from alunduil/alunduil-infrastructure#116)

`git-poi-all` — co-port to Rust, or keep the bash sweeper calling the new binary? Decide before cutting the release: it determines whether the 1.0.0 CLI contract has to stay bash-sweeper compatible.