Adds three named rate limiters to the existing Redis sliding-window
catalog and a withRateLimit wrapper that composes inside withAuth.
Wires the OCR limiter into the receipt-scan endpoint so a runaway
client can't burn through the AI budget in a tight loop.
- ocr: 10/min/user
- ai: 60/min/user (reserved for future server-side AI surfaces)
- exports: 30/hour/user (reserved for GDPR bundle, PDF, CSV exports)
429 responses include X-RateLimit-* headers and a Retry-After hint.
Tests: 771/771 vitest (was 766) — +5 rate-limit tests covering catalog
shape, sliding window, cross-prefix isolation, cross-user isolation,
and resetAt timestamp.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
