docs(skill): document Workers domain conflict recovery

[dxiongya]

Summary

Document the administrator-only recovery contract for a Worker environment quarantined after a Cloudflare custom-domain conflict.

• Adds the exact /api/admin/workers/domain-conflict-recovery endpoint and request shape.
• Documents the existing administrator authorization requirement and fail-closed ownership checks.
• Clarifies that recovery does not detach or delete another Cloudflare service's binding.
• Links the reference from the bundled xapi-workers skill and adds guide coverage tests.

This PR is documentation and skill coverage only. It does not add a regular customer CLI command or change backend behavior.

Validation

• bun install --frozen-lockfile
• bun run typecheck
• bun run build
• bun run test
• npm pack --dry-run --ignore-scripts