docs(standards): add blog post for terragrunt support (#10)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: matthew-on-git

content/blog/2026-03-05-terragrunt-support.md

@@ -0,0 +1,49 @@
+---
+title: "Terragrunt Support"
+date: 2026-03-05
+description: "Terragrunt formatting ships as a companion to Terraform -- automatic detection, no configuration required."
+---
+
+Terragrunt is now included in the dev-toolchain container as a companion tool to Terraform. Projects that use `terragrunt.hcl` files get automatic format checking with zero configuration.
+
+## How It Works
+
+There is no new language entry. Terragrunt runs within the existing `terraform` language block. If your project already declares `terraform` in `.devrail.yml`, Terragrunt formatting is available immediately.
+
+The Makefile detects `terragrunt.hcl` files at runtime:
+
+- **`make format`** runs `terragrunt hclfmt --terragrunt-check` -- exits non-zero if files need formatting
+- **`make fix`** runs `terragrunt hclfmt` -- formats files in place
+
+If no `terragrunt.hcl` files exist, the check is silently skipped. Projects that use Terraform without Terragrunt are unaffected.
+
+```console
+$ make format
+✓ terraform fmt -check -recursive
+✓ terragrunt hclfmt --terragrunt-check
+```
+
+## Why a Companion Tool
+
+Terragrunt is a thin wrapper around Terraform for DRY infrastructure code across multiple modules. It uses its own HCL configuration files (`terragrunt.hcl`) that `terraform fmt` does not process. Adding `terragrunt hclfmt` as a companion means teams get consistent formatting for both file types from a single `make check` invocation.
+
+The alternative -- a separate `terragrunt` language entry in `.devrail.yml` -- would require projects to declare two languages for what is fundamentally one infrastructure stack. The companion approach is simpler: declare `terraform`, and Terragrunt support follows automatically.
+
+## Pre-Commit Hooks
+
+The template repositories include a commented hook for local Terragrunt formatting:
+
+```yaml
+- repo: https://github.com/antonbabenko/pre-commit-terraform
+  rev: v1.96.3
+  hooks:
+    - id: terraform_fmt
+    - id: terraform_tflint
+    # Uncomment if using Terragrunt:
+    # - id: terragrunt_fmt
+```
+
+## Get Started
+
+- [Terraform standards reference](/docs/standards/terraform/) -- includes Terragrunt configuration and Makefile targets
+- [Container tool versions](/docs/container/versions/) -- exact versions shipped in the current image