feat: billing layer v1.3.86 — PostgreSQL statistics

- internal/billing: Store interface + pgStore (pgx/v5 pool) + NoopStore
- factory.go: NewStore() from BILLING_DSN env var (NoopStore fallback)
- Server.billing: injected into Config, initialized in main
- handleInvokeFunction: record invocation (TriggerConsole)
- invokeInternalFunction: record invocation (TriggerHTTP)
- handleCreateFunction: record event_type=create
- handleCloneFunction: record event_type=clone
- handleDeleteFunction: record event_type=delete
- table: invocations (namespace, function_name, trigger_type, duration_ms, status_code...)
- BILLING_DSN added to console.yaml
- pgx/v5 added to go.mod/go.sum

console/internal/billing/factory.go

@@ -0,0 +1,23 @@
+package billing
+
+import (
+	"context"
+	"log"
+	"os"
+)
+
+// NewStore создаёт Store из переменной окружения BILLING_DSN.
+// Если DSN пустой — возвращает NoopStore (статистика отключена, сервер работает нормально).
+func NewStore() Store {
+	dsn := os.Getenv("BILLING_DSN")
+	if dsn == "" {
+		log.Printf("billing: BILLING_DSN not set, statistics disabled")
+		return NoopStore{}
+	}
+	store, err := NewPostgresStore(context.Background(), dsn)
+	if err != nil {
+		log.Printf("billing: failed to connect to PostgreSQL: %v — statistics disabled", err)
+		return NoopStore{}
+	}
+	return store
+}