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/internal/provider/provider.go

@@ -1,3 +1,9 @@
+// Package provider — регистрация Terraform-провайдера Nubes.
+//
+// Определяет:
+//   - New() — создание провайдера с конфигурацией (api_token, api_endpoint)
+//   - Resources() — список всех ресурсов из resources_gen.AllResources()
+//   - Schema() — схема конфигурации провайдера
 package provider
 
 import (