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/noop.go

@@ -0,0 +1,8 @@
+package billing
+
+// NoopStore — заглушка Store, которая тихо игнорирует все записи.
+// Используется когда BILLING_DSN не задан.
+type NoopStore struct{}
+
+func (NoopStore) RecordInvocation(_ Invocation) {}
+func (NoopStore) Close()                        {}