Fix installed scaffolder compiler/runtime version pairing

[ScriptedAlchemy]

Problem

The Version Packages candidate in #411 pairs agent-bundle@0.2.0 with @agent-bundle/runtime@0.1.0. The installed create-agent-bundle scaffolder currently derives the runtime version and packed-tarball suffix from the compiler package spec, so a registry scaffold created with compiler 0.2.0 can request nonexistent or incompatible runtime 0.2.0.

Required contract

• Preserve same-SHA preview pairing for preview package specs.
• For registry/versioned compiler specs, select @agent-bundle/runtime from authoritative compatibility metadata declared by the compiler package (or one generated pairing record), never by copying the compiler version.
• Fail clearly when the installed compiler and selected runtime are incompatible.

Acceptance

• Trace and update every scaffolder caller of the pairing helper.
• Add installed-scaffolder coverage using actual differently-versioned packed tarballs (agent-bundle@0.2.0, @agent-bundle/runtime@0.1.0, and renderer if required).
• Scaffold, install, and build after deleting source inputs.
• Cover a clear incompatible-pair failure.
• Update English and Chinese scaffolder/install docs and add the appropriate changeset.

This issue is intentionally separate from machine-owned Version Packages PR #411. Do not edit, merge, or publish #411; Changesets should regenerate it after the source fix lands.