Phase 5 billing: account-based annual sub + tag SKUs + SMS pool + tag lifecycle

- Schema: plans, orders subscription cols + plan_id + period_started_at,
  billing_events log, users.stripe_id + sms_credits, products.price_aud
  (db/schema.sql + Laravel migration, idempotent)
- Laravel/Cashier: Billable User, checkout (annual sub + one-off SKUs with
  Managed Payments tax_code), webhook controller (signature-verified,
  idempotent, BILLING_ENABLED kill-switch), account tag transitions,
  nightly reconcile, Stripe portal link, PlanResource + billing dashboard
- Go frontend: account-level gating (paid sub required), SMS pool
  (included 50/yr + credits, drawn after included), plan caps replace
  constants, 60s plan cache (credits fresh), 25-tag cap (plan max_tags)
- BillingSeeder: personal plan + 3 SKUs + dev paid orders
- Verified test-mode e2e: subscribe/paid/active/alerts, pool exhaust +
  credits resume, lapsed/suspended, cancelled/closed, recover/active,
  webhook idempotency, 25-cap, one-off SKUs, replacement, kill-switch,
  invalid signature 400

frontend/internal/db/models.go

@@ -8,14 +8,43 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 )
 
+type BillingEvent struct {
+	ID            int64              `json:"id"`
+	StripeEventID string             `json:"stripe_event_id"`
+	EventType     string             `json:"event_type"`
+	OrderID       pgtype.Int8        `json:"order_id"`
+	Payload       []byte             `json:"payload"`
+	CreatedAt     pgtype.Timestamptz `json:"created_at"`
+}
+
 type Order struct {
-	ID        int64              `json:"id"`
-	AccountID pgtype.Int8        `json:"account_id"`
-	Status    string             `json:"status"`
-	CreatedAt pgtype.Timestamptz `json:"created_at"`
-	UpdatedAt pgtype.Timestamptz `json:"updated_at"`
-	Amount    pgtype.Numeric     `json:"amount"`
-	RenewsAt  pgtype.Timestamptz `json:"renews_at"`
+	ID              int64              `json:"id"`
+	AccountID       pgtype.Int8        `json:"account_id"`
+	Status          string             `json:"status"`
+	CreatedAt       pgtype.Timestamptz `json:"created_at"`
+	UpdatedAt       pgtype.Timestamptz `json:"updated_at"`
+	Amount          pgtype.Numeric     `json:"amount"`
+	RenewsAt        pgtype.Timestamptz `json:"renews_at"`
+	StripeID        pgtype.Text        `json:"stripe_id"`
+	PmType          pgtype.Text        `json:"pm_type"`
+	PmLastFour      pgtype.Text        `json:"pm_last_four"`
+	TrialEndsAt     pgtype.Timestamptz `json:"trial_ends_at"`
+	PlanID          pgtype.Int8        `json:"plan_id"`
+	PeriodStartedAt pgtype.Timestamptz `json:"period_started_at"`
+}
+
+type Plan struct {
+	ID              int64              `json:"id"`
+	PlanType        string             `json:"plan_type"`
+	Name            string             `json:"name"`
+	PriceAud        pgtype.Numeric     `json:"price_aud"`
+	BillingInterval string             `json:"billing_interval"`
+	SmsIncluded     int32              `json:"sms_included"`
+	MaxTags         int32              `json:"max_tags"`
+	AlertsPerDay    int32              `json:"alerts_per_day"`
+	AlertsPerHour   int32              `json:"alerts_per_hour"`
+	CreatedAt       pgtype.Timestamptz `json:"created_at"`
+	UpdatedAt       pgtype.Timestamptz `json:"updated_at"`
 }
 
 type Product struct {
@@ -26,6 +55,7 @@ type Product struct {
 	CreatedAt pgtype.Timestamptz `json:"created_at"`
 	UpdatedAt pgtype.Timestamptz `json:"updated_at"`
 	PhotoUrl  pgtype.Text        `json:"photo_url"`
+	PriceAud  pgtype.Numeric     `json:"price_aud"`
 }
 
 type Scan struct {
@@ -78,4 +108,6 @@ type User struct {
 	IsAdmin       bool               `json:"is_admin"`
 	RememberToken pgtype.Text        `json:"remember_token"`
 	Paused        bool               `json:"paused"`
+	StripeID      pgtype.Text        `json:"stripe_id"`
+	SmsCredits    int32              `json:"sms_credits"`
 }