[codex] fix nvim treesitter setup

[marcfranquesa]

Summary

• migrate nvim-treesitter from the archived master setup to main
• enable Tree-sitter via native FileType autocmds and keep parser install/update on the new API
• add tree-sitter to the Homebrew package manifest for parser builds
• trim small Neovim config redundancies and fix existing typos/guards

Root Cause

Neovim 0.12 passes directive captures as node lists, but the pinned old nvim-treesitter markdown injection directive still treated captures as a single node. render-markdown.nvim triggered that injection path on fenced markdown code blocks, causing node:range() to be called on a Lua table.

Validation

• find .config/nvim -name '*.lua' -print0 | xargs -0 -n1 luac -p
• git diff --cached --check
• XDG_CONFIG_HOME=/tmp/dotfiles-codex-fix-nvim-treesitter/.config nvim --headless '+qa!'
• markdown fenced-code parse repro with the PR config: markdown parse ok
• base checkout confirmed clean on main

checkhealth nvim-treesitter now reports only the missing local tree-sitter CLI on this machine; this PR adds that package to bootstrap/pkgs.csv.