docs: add detailed package-level comments to all TOOLS/ and provider/

TOOLS:
- yaml-generator: types (API↔YAML), client (proxy/REST + retry)
- resource-generator: types (3 resource kinds), loader (pipeline),
  writers (generated files), params (merge/CreateOnly/ForceNew)
- docs-generator, ops-generator — already documented

provider:
- main.go: entrypoint + build instructions
- core: API client (GetInstance, RunOperation, GetInstanceState)
- provider: provider registration (New, Resources, Schema)
- resources_core: shared CRUD, state refresh, params, validation

provider/main.go

@@ -1,3 +1,10 @@
+// Terraform-провайдер Nubes Cloud.
+//
+// Регистрирует провайдер в hashicorp/terraform-plugin-framework.
+// Все ресурсы подключаются через resources_gen.AllResources().
+//
+// Сборка: go build -o terraform-provider-nubes .
+// Версия задаётся через ldflags: -ldflags "-X main.version=X.Y.Z"
 package main
 
 import (