test(nvim): add minimal main/master configs

test/nvim/README.md

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+# Neovim test configs
+
+This directory contains minimal Neovim configs for testing `tree-sitter-dotenv` with both
+legacy and rewritten `nvim-treesitter`.
+
+## Files
+
+- `init-main.lua` → `nvim-treesitter` `main` (new API)
+- `init-master.lua` → `nvim-treesitter` `master` (legacy API)
+
+## Run
+
+From the repository root, use isolated app names so test state does not mix:
+
+```bash
+NVIM_APPNAME=ts-dotenv-main nvim -u "$(pwd)/test/nvim/init-main.lua"
+NVIM_APPNAME=ts-dotenv-master nvim -u "$(pwd)/test/nvim/init-master.lua"
+```
+
+## Install parser
+
+Run:
+
+```vim
+:TSUpdate
+:TSInstall dotenv
+```
+
+## Verify
+
+Open a `.env` file and check:
+
+```vim
+:echo &filetype
+```
+
+Expected output: `dotenv`.
+
+### Show the syntax tree
+
+```vim
+:InspectTree
+```