Add event schema extraction to CLI and workflow

[NTCoding]

Deliverable: Event schemas extracted from code and displayed in Eclair

Context

The Riviere schema supports eventSchema on Event components, and Eclair displays it. However:

1. The CLI has no way to add eventSchema when adding Event components
2. The extraction workflow doesn't capture event schemas from TypeScript types

Delivers

1. CLI supports adding eventSchema when creating Event components
2. Extraction workflow captures event schemas from code
3. Demo app extraction produces graphs with event schemas

Acceptance Criteria

• Given Event type, When add-component called with --event-schema, Then eventSchema is set
• Given TypeScript event type definition, When extraction runs, Then eventSchema captured
• Given Eclair, When viewing Event component, Then schema is displayed

Related Code

• packages/riviere-cli/src/commands/builder/add-component.ts
• packages/riviere-schema/src/schema.ts:85

Migrated from Task Master #65