chore(release): bump version to 0.6.2

[lostmartian]

What

Bumps all three distributables to 0.6.2 and cuts the changelog section for #64, which renamed the npm launcher to @kerrshift/agentdiff.

File	Version
src/agentdiff/__init__.py (PyPI agent-trajectory-diff)	0.6.1 → 0.6.2
npm/package.json (npm @kerrshift/agentdiff)	0.6.1 → 0.6.2
plugins/agentdiff/.claude-plugin/plugin.json	0.6.1 → 0.6.2

Why

• npm: this is the release that puts npx @kerrshift/agentdiff on npm. The 0.6.1 npm publish never landed because npm rejected the unscoped name.
• PyPI and the plugin: bumped in step. The launcher pins the PyPI release of its own version, and the tests require all three versions to match.

Roadmap: P1.2.

How

After merge, pushing the v0.6.2 tag runs publish.yml in this order:

1. build;
2. PyPI;
3. npm: version check, launcher tests, then npm publish --provenance --access public;
4. GitHub release.

One thing to check on npm before tagging: the NPM_TOKEN granular token must be allowed to publish under the kerrshift scope. A token set to "All packages" with read and write covers this, as long as your account has a developer or owner role in the kerrshift org.

Testing

make lint                  -> All checks passed
uv run python -m pytest    -> 461 passed (version-sync test included)
cd npm && npm test         -> 4 passed
npm publish --dry-run      -> @kerrshift/agentdiff@0.6.2, public access
uv build                   -> agent_trajectory_diff-0.6.2 wheel + sdist
claude plugin validate --strict .  -> ✔ Validation passed

Checklist

• Exactly one logical change in this PR
• make lint passes
• uv run python -m pytest is green
• Docs updated if user-facing
• CHANGELOG.md entry added under [Unreleased] (if feat/fix)
• Conventional title: type(scope): summary