[codex] Add annotation authoring helpers

[meekmachine]

Closes #109.

Summary

• add shared annotation authoring helpers for cloning, merging, removing, reordering, resetting, and validating annotation regions
• make AnnotationRegion support persisted customPosition so the profile-level authoring shape matches the runtime region behavior more closely
• refactor the preset/profile and character-config extenders to reuse the shared annotation merge logic instead of keeping duplicate implementations
• document annotationRegions as the canonical authored annotation surface while keeping top-level regions as the current runtime/back-compat shape

Why

The package already had most of the annotation data model and runtime extension path, but downstream apps still had to duplicate annotation merge and validation behavior in app code.

This change gives the SliderDrawer-side annotation editor work a package-level contract to build against and removes duplicate merge logic from the existing Loom3 extension helpers.

Validation

• npm test
• npm run typecheck
• npm run build

[meekmachine]

PR backlog triage — CLOSE (abandoned)

Abandoned draft with no active Embody/Polymer consumer. RuntimeCore/bindings work continues elsewhere; lip-sync planners belong in Polymer.

Plan: meekmachine/Polymer#59