[codex] Move moments to the story level

[jhull]

Summary

Moves NCP Moments from narrative-local storytelling into required story.moments[].

Moments are storytelling units: scenes, chapters, sequences, acts, levels, or comparable audience-facing containers. They belong to the story as a whole because a single storytelling unit can carry structural material from multiple narratives at once. For example, one scene can turn the public Objective Story, illustrate a private Relationship Story issue, and echo a Main Character Storypoint without becoming three duplicated scenes.

What changed

• Adds required story.moments[] to the JSON schema and YAML schema twin.
• Adds a reusable story_moment definition.
• Requires story-level Moment references to qualify each storybeat_id and storypoint_id with narrative_id.
• Adds storypoints[] references on Moments alongside storybeats[].
• Removes narratives[].storytelling.moments[] from the schema so Moments have one unambiguous home.
• Migrates existing examples to story-level Moments.
• Adds examples/cross-narrative-moments.json to demonstrate one Moment referencing Storybeats and Storypoints from two narratives.
• Adds invalid fixtures proving story-level Storybeat references must include narrative_id and narrative-local Moments are rejected.
• Updates SPECIFICATION.md, schema reference docs, history, README, and copyright example.

Why

The previous shape implied that a Moment belonged to exactly one narrative because it lived at narratives[].storytelling.moments[]. That is too narrow for actual storytelling. A scene is experienced by the audience as part of the whole story, and it can legitimately relate to structural elements from different narratives.

Putting Moments only on story.moments[] preserves that audience-facing reality while keeping formal narrative structure intact. The Moment gathers references. The narrative_id on each reference tells consumers which narrative owns the Storybeat or Storypoint.

Having both story.moments[] and narratives[].storytelling.moments[] would create ambiguous ownership and invite duplicated or conflicting exports. This PR makes the model explicit: narratives own structure; the story owns storytelling Moments.

Compatibility

This is a schema-shape change for canonical exports because story.moments[] is now required and narratives[].storytelling.moments[] is no longer valid.

Importers that still receive older nested Moment payloads should migrate those entries up to story.moments[] and add narrative_id to each referenced Storybeat or Storypoint.

Validation

• node tests/validate-schema.js -> Schema validation checks passed (8 valid + 11 invalid fixtures).
• ruby -rjson -ryaml -e "json = JSON.parse(File.read('schema/ncp-schema.json')); yaml = YAML.load_file('schema/ncp-schema.yaml'); abort('schema mismatch') unless json == yaml; puts 'schema JSON/YAML equivalent'" -> schema JSON/YAML equivalent
• git diff --check -> clean