Is your feature request related to a problem? Please describe.
Our docs/examples use free-form tenant ids, but API schemas require UUIDs, causing first-run failures.

Describe the solution you'd like

• Relax tenantId schema to type: string in: POST /v1/events/ingest, GET /v1/events, GET /v1/usage/current, POST /v1/usage/projection, reconciliation routes.
• Keep server-side validation/logging; doc guidance for stable tenant ids.

Acceptance Criteria

• Schemas updated; tests adjusted.
• README/examples remain valid.
• No behavior change besides validation.