chore(release): 0.2.0

[b2m9]

Bumps package.json from 0.1.1 to 0.2.0. Minor rather than patch because
behaviour changed since 0.1.1: explicitly empty containers now materialize
(#12), and malformed option containers are rejected at merger creation (#11).

Release checklist steps 2-4 done: vp install --frozen-lockfile,
vp run check, and npm pack --dry-run all pass (126 tests, 15 files,
24.8 kB). Tagging v0.2.0 and publishing the GitHub Release are the
maintainer's steps after this merges.

🤖 Generated with Claude Code

---

Summary by cubic

Updates @b2m9/keyfold from 0.1.1 to 0.2.0 to reflect behavior changes. Previously, explicitly empty containers did not materialize; now they materialize. Previously, merger creation allowed malformed option containers; now creation fails early with an error.

Migration

• If you relied on empty containers being ignored, handle materialized empty containers in the output state.
• Validate option containers before creating a merger; fix or remove malformed inputs to avoid errors.

Rollout

• After merge, tag v0.2.0 and publish the GitHub Release.

^{Written for commit 6238e62. Summary will update on new commits.}