Specify ontology regression cases that expect no property binding

[virtue039]

A regression case currently requires an expected property, so a person cannot record that an open statement should bind to nothing. The review of #1184 identified this gap with 不再负责 bound to responsibleFor.

This documentation-only PR proposes the next boundary in decision 0061, following the issue-first discussion in #1103 and CONTRIBUTING's requirement to land the contract before implementing data-model or API changes. Existing positive requests remain valid; an explicit expected_binding: "none" request has no target property or direction. The revision specifies nullable-target integrity and retry uniqueness, none versus undecided comparisons, workbench visibility, and acceptance through ordinary alignment without an evaluator or extra job.

The proposal preserves #1103's human-bound exception and explicitly asks whether it should instead apply only to positive expectations. An ending is included as an acceptance control: the review example does not imply that every negated or ended relationship must be unbound.

Validation: inspected the existing migration 0109, add/view/record paths, phrase_bindings::stale and the 0061 boundaries on macOS, based on dev 25fa9f4; git diff --check passes for commit 9350df0. One ADR changes (+78 lines); no production code or migration changes, so runtime suites were not run. The overall 0061 status remains In progress and this new section is explicitly proposed; implementation and real-model acceptance remain open.

Refs #1103, #1184.