feat: build core API, fraud engine, notifier, and frontend

Phase 1 — Core API (Go):
- Events, guests, tokens, RSVPs CRUD on PostgreSQL via pgx/v5
- HMAC-signed per-guest tokens with format validation
- Health endpoint with DB ping, slog JSON logging, graceful shutdown

Phase 2 — NATS + Fraud Engine:
- NATS JetStream pub/sub with explicit-ack consumers
- Python/FastAPI fraud engine with heuristic risk scoring
  (fingerprint mismatch, IP change, missing signals, repeated access)
- gRPC sync scoring with 250ms fail-open timeout
- Per-guest baseline tracking; risk bands low/medium/high/block

Phase 3 — Notifications + Frontend:
- Notification worker scaffolding (Twilio/SES stubs, retry/backoff)
- Nuxt 3 frontend with Tailwind dark theme + brand green
- Live monitor via WebSocket with auto-reconnect
- Activity history endpoint backfills monitor with RSVPs +
  scored access checks (including blocked attempts)

UX polish:
- Marketing-friendly landing page (hero mockup, how-it-works,
  features, use cases, testimonials, FAQ, final CTA)
- Animated layered card mockups on landing + new-event page
- Plus-ones stepper, RSVP status badges, filter buttons
- Friendly access-check labels (Verified/Review/Suspicious/Blocked)
- Dashboard hydration fix via ClientOnly wrapper

Infrastructure:
- docker-compose for full local dev (postgres, nats, api,
  fraud-engine, notifier, frontend)
- Multi-stage Dockerfiles, non-root UID 1000
- Integration tests with testcontainers-go

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/domain/rsvp.go

@@ -0,0 +1,41 @@
+package domain
+
+import (
+	"errors"
+	"time"
+
+	"github.com/google/uuid"
+)
+
+type RSVPResponse string
+
+const (
+	RSVPAttending RSVPResponse = "attending"
+	RSVPDeclined  RSVPResponse = "declined"
+	RSVPMaybe     RSVPResponse = "maybe"
+)
+
+func (r RSVPResponse) Valid() bool {
+	switch r {
+	case RSVPAttending, RSVPDeclined, RSVPMaybe:
+		return true
+	}
+	return false
+}
+
+type RSVP struct {
+	ID                uuid.UUID      `json:"id"`
+	GuestID           uuid.UUID      `json:"guest_id"`
+	Response          RSVPResponse   `json:"response"`
+	PlusOnes          int            `json:"plus_ones"`
+	DietaryNotes      *string        `json:"dietary_notes,omitempty"`
+	SubmittedAt       time.Time      `json:"submitted_at"`
+	DeviceFingerprint map[string]any `json:"device_fingerprint,omitempty"`
+	IPAddress         *string        `json:"ip_address,omitempty"`
+	RiskScore         *int           `json:"risk_score,omitempty"`
+}
+
+var (
+	ErrRSVPAlreadySubmitted = errors.New("rsvp already submitted")
+	ErrRSVPBlocked          = errors.New("rsvp blocked due to fraud risk")
+)