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/core/editors/Glossary.md

@@ -0,0 +1,73 @@
+# Editors Glossary
+
+### LSP - Language Server Protocol
+
+> https://en.wikipedia.org/wiki/Language_Server_Protocol
+
+> https://langserver.org/
+
+The Language Server Protocol (LSP) is an open, JSON-RPC-based protocol for use between source code
+editors or integrated development environments (IDEs) and servers that provide programming
+language-specific features like:
+
+- motions such as go-to-definition, find-references, hover.
+- **code completion**
+- **marking of warnings and errors**
+- **refactoring routines**
+- syntax highlighting (use Tree-sitter instead)
+- code formatting (use a dedicated formatter instead)
+
+The goal of the protocol is to allow programming language support to be implemented and distributed
+independently of any given editor or IDE.
+
+LSP was originally developed for Microsoft Visual Studio Code and is now an open standard. In the
+early 2020s LSP quickly became a "norm" for language intelligence tools providers.
+
+### Tree-sitter
+
+> https://tree-sitter.github.io/tree-sitter/
+
+> https://www.reddit.com/r/neovim/comments/1109wgr/treesitter_vs_lsp_differences_ans_overlap/
+
+Tree-sitter is a parser generator tool and an **incremental parsing** library. It can build a
+concrete syntax tree for a source file and efficiently update the syntax tree as the source file is
+edited.
+
+It is used by many editors and IDEs to provide:
+
+- **syntax highlighting**
+- **indentation**
+- **creating foldable code regions**
+- **Incremental selection**
+- **simple refactoring in a single file**
+  - such as join/split lines, structural editing, cursor motion, etc.
+
+**Treesitter process each file independently**, and it is not aware of the semantics of your code.
+For example, it does not know does a function/variable really exist, or what is the type/return-type
+of a variable. This is where LSP comes in.
+
+The LSP server parses the code much more deeply and it **not only parses a single file but your
+whole project**. So, the LSP server will know whether a function/variable does exist with the same
+type/return-type. If it does not, it will mark it as an error.
+
+**LSP does understand the code semantically, while Treesitter only cares about correct syntax**.
+
+#### LSP vs Tree-sitter
+
+- Tree-sitter: lightweight, fast, but limited knowledge of your code. mainly used for **syntax
+  highlighting, indentation, and folding/refactoring in a single file**.
+- LSP: heavy and slow on large projects, but it has a deep understanding of your code. mainly used
+  for **code completion, refactoring in the projects, errors/warnings, and other semantic-aware
+  features**.
+
+### Formatter vs Linter
+
+Linting is distinct from Formatting because:
+
+1. **formatting** only restructures how code appears.
+   1. `prettier` is a popular formatter.
+1. **linting** analyzes how the code runs and detects errors, it may also suggest improvements such
+   as replace `var` with `let` or `const`.
+
+Formatters and Linters process each file independently, they do not need to know about other files
+in the project.