feat: prepare OpenBackpack 0.1.0 and governed OIDC releases

[GrahamQuan]

Summary

• add the initial OpenBackpack CLI, core library, AI SDK adapter, schemas, tests, and technical documentation
• publish the CLI as openbackpack and prepare @openbackpack/core and @openbackpack/ai
• add fixed-group Changesets versioning with an initial 0.1.0 changeset
• add SHA-pinned CI and an npm Trusted Publishing workflow using GitHub OIDC, with no long-lived npm token
• validate package metadata, built entry points, tarball contents, and removal of workspace: protocols
• document rebase-only repository governance and owner-only bypass semantics

Impact

After merge, CI exposes the stable quality check. npm publishing remains fail-closed behind NPM_RELEASE_ENABLED; the
two new scoped package records must be bootstrapped before Trusted Publishers can be configured and the release window
opened.

Validation

• pnpm check
• pnpm exec changeset status
• git diff --check
• workflow YAML parse check
• tarball checks for all three publishable packages