security(home): drop all neovim plugins to shrink supply-chain exposure (#259)

* chore(home): drop AstroNvim bundle and centralize editors

Remove the bundled Neovim plugin tree to shrink supply-chain exposure; keep a
minimal programs.neovim backup. Daily editing stays Helix-first with Yazi and
Zellij.

- Add Helix/Neovim docs, glossary, and cheatsheets under core/editors/.
- Default EDITOR/VISUAL to hx; use SUDO_EDITOR nvim --clean for sudoedit and
  other sensitive edits; adjust Nushell buffer_editor accordingly.
- Apply Helix Home Manager settings (keys, editor UI) in core/editors/helix.
- Keep heavy language-server tooling only in home/base/tui/editors/packages.nix;
  wire it via an explicit default.nix import so core stays lightweight.
- Extend modules/base packages.nix where that profile sets global editor env.

* docs: link editors, VS Code, and agents from README

Document tui/editors versus core/editors; add root README pointers to GUI
vscode (Home Manager) and agents/. Cross-link heavy packages README from
core/editors.

home/base/tui/editors/neovim/nvim/lua/polish.lua

@@ -1,16 +0,0 @@
--- This will run last in the setup process and is a good place to configure
--- things like custom filetypes. This just pure lua so anything that doesn't
--- fit in the normal config locations above can go here
-
--- Set up custom filetypes
--- vim.filetype.add {
---   extension = {
---     foo = "fooscript",
---   },
---   filename = {
---     ["Foofile"] = "fooscript",
---   },
---   pattern = {
---     ["~/%.config/foo/.*"] = "fooscript",
---   },
--- }