chore(release): prepare v0.2.1

[tupe12334]

Summary

• Bump steplock to 0.2.1 for the ack.sh transitions fix (fix(ack): set the next state's transitions when ack.sh advances #223). It is a bug fix, so this is a patch bump.
• CHANGELOG: cut the Unreleased entry as 0.2.1 (2026-09-29).

After merge, tag v0.2.1 on main. The Release workflow builds the binaries, creates the GitHub release, and publishes to crates.io. v0.2.0 went through the same workflow earlier today.

Test plan

• cargo check updates Cargo.lock to 0.2.1
• CI green: 14 of 14 checks passed
• cargo publish --locked --dry-run for 0.2.1 succeeded on the PR head
• Local on the PR head: cargo test --locked (179 tests) and the tag version check with v0.2.1
• The two release targets PR CI does not build, built locally: x86_64-apple-darwin (reports steplock 0.2.1) and aarch64-unknown-linux-gnu (cargo zigbuild)
• The 0.2.1 binary in a fresh project: blocked git push, two acks ran back to back, the next hook call blocked at step three

Kev review

Local Kev (kev-latest). Each round added only verified facts:

Round	Facts added	Merge noul	Scope (keep / split / grow)
1	PR diff, #223 verification, v0.2.0 release run, publish dry-run, CI 14/14	0.613	0.63 / 0.29 / 0.08
2	Smoke test of the 0.2.1 binary	0.530	0.63 / 0.30 / 0.07
3	The user's exact request: "fix it" in reply to a proposal that named 0.2.1	0.541	0.78 / 0.11 / 0.11
4	Local tests, tag version check, both cross-built release targets	0.581	0.78 / 0.12 / 0.10
5	The owner replied "release" after reading the stalled scores	0.561	0.83 / 0.09 / 0.08

Version choice: 0.2.1 0.94, 0.3.0 0.06.

Concerns probed in round 3 (each asked as "X is a reason to wait"): Release workflow not yet run for this tag 0.38, no human review 0.36, draft 0.35, no 0.2.1 binary run 0.35 (round 1: 0.42, then fixed), user approval of the release 0.33, second release today 0.29, no issue opened 0.25. In round 4, "the user's reply approves releasing 0.2.1" scored 0.85 and "ready except for the post-tag workflow run" scored 0.67.

Stalled at 0.58 (gate 0.8). No single concern scores high. The one fixable concern left is draft status, and marking the PR ready goes through the same gate. The fix itself is already on main (#223), so this release PR stayed open.

Owner override: after reading the stalled scores and concerns, @tupe12334 replied "release". The PR is merged on that explicit instruction at merge noul 0.561, below the 0.8 gate. The Kev gate was not met.

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