release: v0.6.0

[github-actions]

Machine-generated release PR for v0.6.0, base commit A = 8195a40ee0aa982d3002e783ad34ab6221f90b89,
opened by release-build run 32661789098. Process:
docs/ai/design/release-process.md.

Two machine-written commits:

1. d18fe5967a7407035fd17909abf14dc60ef125a7 -- commit B, the tag target: the binary-default release
   Package.swift (asset URL + checksum of the built XCFramework) plus
   release-manifest.json, the provenance record that release-publish
   re-verifies at tag time. Review it here: 8195a40...d18fe59
2. commit R -- restores Package.swift to A's copy verbatim, so every tip
   of main stays a source-only package. The PR's net diff is
   release-manifest.json only.

To ship v0.6.0:

1. Review B via the compare link above (the URL and checksum lines).
2. Merge this PR using "Create a merge commit" -- not squash, not
   rebase. Only a true merge preserves B in main's ancestry; publish
   refuses the tag otherwise. If it was squashed or rebased anyway, recover
   with a history-only merge:
   git fetch origin && git checkout main && git pull && git merge -s ours origin/release-prep/v0.6.0 && git push origin main,
   then push the tag.
3. After the merge, push the tag at B -- the tag push is the approval and
   the only trigger for publishing:

git fetch origin
git tag v0.6.0 d18fe5967a7407035fd17909abf14dc60ef125a7
git push origin v0.6.0

Do not tag before merging: publish requires B to be an ancestor of main.
release-publish then re-verifies everything in release-manifest.json
(checks 1-6) and publishes the GitHub Release with the already-built,
already-checksummed artifacts. No rebuild.

Notes:

• CI does not run on this PR: it was pushed with the workflow token,
  whose events GitHub never lets trigger other workflows. CI validated
  A on its own PR, and release-build built and checksummed A.
• The tag must be pushed within 90 days of the build (artifact
  retention); after that, re-dispatch release-build for a fresh B.
• This branch can be deleted once the tag is pushed; B stays reachable
  from main and from the tag.