New releases json validate command; schema moved to v2

c1e5ee6: Add releases json validate <path> — validate a releases.json v2 owner manifest against the published schema (ReleasesJsonConfigSchema) before publishing it. Accepts a file path or - for stdin, detects the hosting scope (domain vs repo) for readable path-anchored errors, and supports --json for machine output (exit 0 valid / 1 invalid). The domain form (live fetch + materialization plan) is deferred until the public dry-run endpoint lands (buildinternet/releases#1910) so web and CLI share one verdict.

cf95da6: Adopt @buildinternet/releases-api-types 0.37.0 (releases.json v2 schema) and migrate the repo-root releases.json to the v2 manifest format (product binding + github: "self" release locator).