feat(nvim): add terraform LSP and tooling support

[maybebyte]

Summary

Adds full Terraform tooling support to the Neovim config so .tf and
.tfvars files get the same treatment as every other supported language:

• LSP: terraform-ls (HashiCorp) auto-installed via
  mason-tool-installer; auto-enabled by mason-lspconfig with
  defaults; inherits the global '*' capabilities and the existing
  LspAttach keymap/inlay-hint logic.
• Formatter: terraform_fmt wired into conform.nvim for both
  terraform and terraform-vars filetypes (shells out to
  terraform fmt -; CLI itself is manual-install).
• Linter: tflint wired into nvim-lint; installed via Mason.
• Treesitter: terraform and hcl parsers added to
  ensure_installed; .tfvars buffers reuse the terraform parser
  via vim.treesitter.language.register("terraform", "terraform-vars").

Two subtleties caught during verification

1. Empty .tf files don't get the terraform filetype. Neovim's
   built-in detect.tf inspects file content and falls back to the
   legacy tf filetype when the buffer is empty or comment-only, which
   prevents terraform-ls from attaching to fresh files. Fixed via a
   new lua/my/settings/filetypes.lua that forces *.tf -> terraform
   unconditionally.

2. tflint runs as both an LSP and an nvim-lint linter. When the
   Mason tflint package is installed, mason-lspconfig's
   automatic_enable picks it up as a language server (lspconfig has a
   tflint server definition that wraps tflint --langserver). That
   produces duplicate diagnostics alongside the nvim-lint runner.
   mason-lspconfig.setup() now passes
   automatic_enable = { exclude = { "tflint" } } so linting stays in
   nvim-lint where the rest of the project's linters live.

Files

• lua/my/plugins/mason-tool-installer.lua — terraformls + tflint
  added; header comment notes terraform CLI as manual-only
• lua/my/plugins/lspconfig.lua — automatic_enable exclude for
  tflint
• lua/my/plugins/conform.lua — terraform + terraform-vars in
  ft lazy-load and formatters_by_ft
• lua/my/plugins/nvim-lint.lua — terraform = { "tflint" }
• lua/my/plugins/treesitter.lua — hcl + terraform parsers and
  terraform-vars language register
• lua/my/settings/filetypes.lua (new) + init.lua wire-up — forces
  .tf -> terraform to bypass content-based detection
• README.md — Formatters/Linters tables updated;
  tflint --init note added

Test plan

Verified end-to-end on a clean Neovim instance:

• .tf (empty file) → filetype terraform; terraformls
  attaches
• .tfvars → filetype terraform-vars; treesitter highlighter
  active (proves language.register worked); terraformls
  attaches
• terraform-ls and tflint auto-installed via
  mason-tool-installer on VimEnter
• treesitter parsers terraform and hcl installed
• nvim-lint linters_by_ft.terraform == { "tflint" }
• conform formatters_by_ft.terraform == { "terraform_fmt" }
  and same for terraform-vars
• Only terraformls attaches to a .tf buffer (the tflint LSP
  duplicate is correctly suppressed)

Outstanding

terraform CLI is not in the Mason registry, so format-on-save is a
no-op until the user installs it via system package manager / tfenv
/ asdf. Documented in both the mason-tool-installer header comment
and the README Formatters table.

[maybebyte]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

🤖 Generated with Claude Code