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/Structured-Editing.md

@@ -1,23 +0,0 @@
-# Structured Editing
-
-## S-expression data(Lisp)
-
-- paredit/[lispy](https://github.com/doomemacs/doomemacs/tree/master/modules/editor/lispy): too
-  complex.
-- [evil-cleverparens](https://github.com/emacs-evil/evil-cleverparens): simple and useful.
-- [parinfer(par-in-fer)](https://shaunlebron.github.io/parinfer/): modern, simple, elegant and
-  useful, but works not well with some other completion plugins...
-  - to make parinfer works, you should disable sexp & smartparens in any lisp mode.
-
-Some plugins:
-
-- Neovim
-  - [parinfer-rust](https://github.com/eraserhd/parinfer-rust)
-  - <https://github.com/Olical/conjure>
-- Helix
-  - [parinfer #4090 - Helix](https://github.com/helix-editor/helix/discussions/4090)
-
-## Other Languages
-
-1. treesitter
-1. ...