[codex] Scaffold modular Terraform infrastructure layer

[martinhohoff]

What changed

• replaced the old one-off Terraform scaffold with a modular infra/terraform/modules/ plus infra/terraform/envs/dev and infra/terraform/envs/prod layout
• added starter Terraform modules for AWS foundation, Snowflake foundation, and GitHub integration placeholders
• added provider configuration, outputs, remote-state placeholders, variable files, example tfvars, and README guidance for both environment roots
• added bootstrap-friendly terraform-fmt and terraform-validate targets in the root Makefile
• committed Terraform lockfiles after successful initialization and validation of both environment roots
• cleaned up the leftover legacy infra/terraform/environments/ path and normalized stale references

Why it changed

The repository needed a practical v1 infrastructure foundation that matches the selected stack decisions: AWS as the cloud foundation, Snowflake as the primary warehouse, Terraform as the IaC tool, and a single-repo layout that is environment-aware without being enterprise-bloated.

Impact

Contributors now have a clear Terraform entrypoint for dev and prod, reusable module boundaries, safe placeholders for real environment details, and bootstrap commands for format and validation.

Validation

• python3 scripts/validate_repo.py
• make terraform-fmt
• make terraform-validate