Rate limiting — Phase 3 (Automation, client charts, billing, docs)

Complete the MVP with automation and customer-facing features.

## Scope

### Automation
- Automated customer emails:
- Grace notifications.
- Enforcement notifications.
- Upgrade prompts.

### Billing / subscription integration
- Automated tier upgrades and notification to billing team to update invoices.
- Automated state transitions driven by p95 rules.

### Documentation and transition
- Admin guide for configuring global limits, tiers, overrides, tokens, and CIDR lists.
- API documentation for identity/credential handling and rate-limit headers.
- Runbooks for monitoring and responding to limit breaches.
- Knowledge-transfer session with Foundation staff.
- Future recommendations list for long-term improvements.

## Acceptance criteria
- Customers receive automated emails on state change events.
- Customers can view daily and historical usage with limits and p95.
- Tier upgrades flow through billing/subscription and update limits automatically.
- State transitions follow rules without manual admin action.
- Docs and runbooks are published and reviewed internally.
- Knowledge transfer completed.

## Target
TBD