Companion doc to API_V2_PLAN.md describing PR 1: stand up router/v2/ empty but
wired next to a frozen /api/v1, with a trivial GET /api/v2/version to make the
mount testable and no behavior change. Includes the file tree, the api.router.js
/ v2.router.js wiring, empty capability-router stubs, and acceptance criteria.
Adds a forward link from the plan's PR-1 line to the skeleton doc.
Co-Authored-By: Claude <noreply@anthropic.com>
