refactor: improve Neovim/Nix config for quant econ workflow

Consolidates a multi-pass refactor and a set of workflow integrations
tailored to a quantitative economics research workflow (R / Python /
Quarto / LaTeX heavy, reproducibility-conscious). The existing terminal
setup is preserved (snacks.nvim was deliberately not adopted).

=== Structural refactors ===
* Replace the `_G.Config` global with a proper `require('config')` Lua
  module. `_G.Config` is kept only as a backward-compatible alias.
* Split the monolithic `plugin/10_keymap.lua` into domain-specific
  files under `lua/keymap/` (core, helpers, leader, terminal, repl).
* Harden `lua/nix_smart_send.lua` `send_repl`: only skip forward on
  comment nodes, and return cleanly when there is no next sibling.
* Add a filetype-aware REPL dispatcher in `lua/keymap/repl.lua`:
  pure R scripts -> R.nvim, .qmd/.Rmd chunks -> quarto.runner,
  everything else -> vim-slime. Prefer `quarto.runner.run_line()`
  when available and fall back to `run_cell()`.
* Add R Treesitter text objects (function / call / assignment) for
  faster motion when sending code to the REPL.
* Add `+Send` and `+Debug` leader-clue groups for the new prefixes.

=== LSP and tooling ===
* Register `yamlls` for Quarto YAML frontmatter (`plugin/25_lsp.lua`).
* Register `texlab` and add `vimtex` for a real `.tex` workflow
  (`plugin/25_lsp.lua` + new `plugin/28_latex.lua`).
* Wire `nvim-dap` with an R adapter backed by `vscDebugger`
  (new `plugin/26_dap.lua`, gated to the `r` cat).
* Add `image-nvim` for in-editor plots, gated to the `r`/`markdown`
  cats (new `plugin/27_image.lua`).
* Wire `lintr` into `nvim-lint` for R / Quarto (`plugin/22_languages.lua`).
* Add Treesitter parsers for `stata`, `matlab`, `bibtex` for completeness.

=== Nix updates ===
* Pin `python313Packages.pylatexenc` -> `python3Packages.pylatexenc`
  so the markdown cat survives nixpkgs Python default shifts.
* Add `texlab`, `imagemagick`, `luaPackages.magick` to the markdown
  cat so `image.nvim` has a working backend.
* Add `vscDebugger` and `lintr` to the R package list.

=== Misc ===
* Prefer the R.nvim v1.0 Lua API (`require('r.run').send_line()` /
  `send_selection()`); keep `<Plug>` mappings as a fallback so older
  downstream builds don't regress.
* Use `alejandra` (already installed) as the nixd / nil_ls formatter.

Files: 14 modified, 5 added (953 insertions, 490 deletions).

Local verification before merge:
1. `nix flake check --no-build`
2. `nvim --headless -u NONE -l tests/init.lua`
3. Open a `.qmd` -> confirm `yamlls` attaches and `image.nvim` renders.
4. Open an `.R` -> `<leader>db`, `<leader>dc` confirm DAP loads.
5. Open a `.tex` -> confirm `texlab` + `vimtex` are active.

modules/module/specs/plugins.nix

@@ -3,7 +3,53 @@
   pkgs,
   lib,
   ...
-}: {
+}:
+let
+  parserList = [
+    "bash"
+    "bibtex"
+    "c"
+    "cpp"
+    "csv"
+    "diff"
+    "dockerfile"
+    "git_config"
+    "git_rebase"
+    "gitattributes"
+    "gitcommit"
+    "gitignore"
+    "html"
+    "javascript"
+    "json"
+    "julia"
+    "latex"
+    "lua"
+    "luadoc"
+    "make"
+    "markdown"
+    "markdown_inline"
+    "matlab"
+    "nix"
+    "python"
+    "query"
+    "r"
+    "rnoweb"
+    "regex"
+    "sql"
+    "stata"
+    "toml"
+    "vim"
+    "vimdoc"
+    "xml"
+    "yaml"
+    "zig"
+  ];
+in {
+  options.settings.treesitter_parsers = lib.mkOption {
+    type = lib.types.listOf lib.types.str;
+    default = parserList;
+    description = "Tree-sitter parser names to install when the treesitterParsers category is enabled.";
+  };
 
   config.specs.gitPlugins = lib.mkIf (config.cats.gitPlugins or false) {
     data = [];
@@ -94,6 +140,7 @@
     data = with pkgs.vimPlugins; [
       quarto-nvim
       render-markdown-nvim
+      vimtex
       {
         data = otter-nvim;
         pname = "otter";
@@ -125,42 +172,7 @@
   };
 
   config.specs.treesitterParsers = lib.mkIf (config.cats.treesitterParsers or false) {
-    data = with pkgs.vimPlugins.nvim-treesitter-parsers; [
-      bash
-      c
-      cpp
-      csv
-      diff
-      dockerfile
-      git_config
-      git_rebase
-      gitattributes
-      gitcommit
-      gitignore
-      html
-      javascript
-      json
-      julia
-      latex
-      lua
-      luadoc
-      make
-      markdown
-      markdown_inline
-      nix
-      python
-      query
-      r
-      rnoweb
-      regex
-      sql
-      toml
-      vim
-      vimdoc
-      xml
-      yaml
-      zig
-    ];
+    data = map (name: pkgs.vimPlugins.nvim-treesitter-parsers.${name}) config.settings.treesitter_parsers;
   };
 
   config.specs.utils-lazy = lib.mkIf (config.cats.utils or false) {
@@ -177,6 +189,7 @@
       nvim-dap-virtual-text
       nvim-lint
       vim-slime
+      image-nvim
     ];
   };