[codex] add cinematic chat stage

[numnx]

Summary

Adds a cinematic 3D chat mode to the dashboard, backed by richer agent avatar expressions and structured Code UX widget rendering for status, task, sprint, metrics, and action blocks.

What changed

• Added the 3D Chat tab and full-bleed cinematic chat stage.
• Added stage widget parsing/rendering and agent mood selection utilities.
• Expanded agent avatar expressions and lazy scene support for the stage experience.
• Updated chat prompt instructions so assistant replies can emit rich codeux:* fenced JSON widgets.
• Added dashboard tests for stage widgets, agent mood behavior, and accessibility coverage.
• Updated dashboard design-system documentation for the cinematic chat surface.

Validation

pnpm run lint
pnpm run test:dashboard
pnpm run build

All listed checks passed locally.