chore: remove leftover main.tf file and update repository structure

- Remove main.tf from root directory (leftover debug file from previous Multipass experiments)
- Update README.md repository structure section to reflect the removal
- OpenTofu configurations are properly organized in templates/tofu/lxd/ directory

Author: josecelano

README.md

@@ -284,7 +284,6 @@ The repository includes comprehensive GitHub Actions workflows for CI testing:
 ├── target/                 # 🦀 Rust build artifacts (git-ignored)
 ├── Cargo.toml             # Rust workspace configuration
 ├── Cargo.lock             # Rust dependency lock file
-├── main.tf                # Root OpenTofu configuration
 ├── cspell.json            # Spell checking configuration
 ├── project-words.txt      # Custom dictionary for spell checking
 ├── .markdownlint.json     # Markdown linting configuration