Optimize pureintent eval time (Ralph) (#117)

* docs: Ralph report scaffolding + pureintent eval baseline (10.87s)

* cycle-1: drop nixvim — pureintent eval 10.87s → 6.98s (-36%)

nixvim's home-manager module system is by far the dominant cost of
evaluating `nixosConfigurations.pureintent`: a profile of selective
imports puts it at 3.97s of the 10.87s baseline (~36%).

Replace it with a minimal `programs.neovim.enable = true` configuration.
The runtime behaviour of `nvim` changes (no plugins, no LSP, no
mapleader/telescope/treesitter/etc.) — accepted by the user.

Measured on srid-nc (nixos, 6.12.85 kernel), 7 warm-cache runs with
`--option eval-cache false`:

  baseline: 10.85 10.86 10.86 10.87 10.87 10.88 10.91 -> median 10.87s
  cycle-1:  6.94  6.96  6.98  6.98  7.02  7.02  7.73 -> median 6.98s

Other configurations still evaluate:
  - nixosConfigurations.naiveintent
  - darwinConfigurations.infinitude-macos
  - homeConfigurations."srid@zest"

Removes flake input `nixvim` (+ its `flake-parts`, `nixpkgs`, `systems`
sub-inputs from the lock).

* docs: wrap up Ralph report (10.87s -> 6.99s = -35.7%)

7 dead-ends documented so they don't have to be re-tried. Key
finding: after dropping nixvim (cycle 1), the eval floor is
home-manager's per-entry submodule materialisation
(systemd.user.services / programs.ssh.matchBlocks), not the
option-declaration count of any wrapper module. Inlining
jumphost-nix or vira moves the cost; it does not eliminate it.

modules/flake-parts/nixos-flake.nix

@@ -16,7 +16,6 @@
         "nix-darwin"
         # "nixos-hardware"
         "nix-index-database"
-        "nixvim"
       ];
     };
   };

modules/home/editors/neovim/default.nix

@@ -1,127 +1,9 @@
-{ flake, pkgs, ... }:
-
-let
-  inherit (flake) inputs;
-in
+{ ... }:
 {
-  imports = [
-    inputs.nixvim.homeModules.nixvim
-  ];
-  programs.nixvim = {
+  programs.neovim = {
     enable = true;
     defaultEditor = true;
-
-    imports = [
-      ./nvim-tree.nix
-      ./lazygit.nix
-    ];
-
-    # Theme
-    colorschemes.rose-pine.enable = true;
-
-    # Settings
-    opts = {
-      expandtab = true;
-      shiftwidth = 2;
-      smartindent = true;
-      tabstop = 2;
-      number = true;
-      clipboard = "unnamedplus";
-      termguicolors = true;
-    };
-
-    # Keymaps
-    globals = {
-      mapleader = " ";
-    };
-
-    extraPlugins = [
-      pkgs.vimPlugins.outline-nvim
-    ];
-
-    plugins = {
-      # UI
-      web-devicons.enable = true;
-      lualine.enable = true;
-      bufferline.enable = true;
-      treesitter = {
-        enable = true;
-      };
-      haskell-scope-highlighting.enable = true;
-      which-key = {
-        enable = true;
-      };
-      noice = {
-        # WARNING: This is considered experimental feature, but provides nice UX
-        enable = true;
-        settings.presets = {
-          bottom_search = true;
-          command_palette = true;
-          long_message_to_split = true;
-          #inc_rename = false;
-          #lsp_doc_border = false;
-        };
-      };
-      telescope = {
-        enable = true;
-        keymaps = {
-          "<leader>ff" = {
-            options.desc = "file finder";
-            action = "find_files";
-          };
-          "<leader>fr" = {
-            options.desc = "recent files";
-            action = "oldfiles";
-          };
-          "<leader>fg" = {
-            options.desc = "find via grep";
-            action = "live_grep";
-          };
-          "<leader>T" = {
-            options.desc = "switch colorscheme";
-            action = "colorscheme";
-          };
-        };
-        extensions = {
-          file-browser.enable = true;
-          ui-select.enable = true;
-          frecency.enable = true;
-          fzf-native.enable = true;
-        };
-      };
-
-      # LSP
-      # https://github.com/nix-community/nixvim/blob/main/plugins/lsp/default.nix
-      lsp = {
-        enable = true;
-        keymaps = {
-          lspBuf = {
-            "gd" = "definition";
-            "gD" = "references";
-            "gt" = "type_definition";
-            "gi" = "implementation";
-            "K" = "hover";
-            "<leader>A" = "code_action";
-          };
-          diagnostic = {
-            "<leader>k" = "goto_prev";
-            "<leader>j" = "goto_next";
-          };
-        };
-        servers = {
-          hls = {
-            enable = true;
-            installGhc = false;
-          };
-          marksman.enable = true;
-          nil_ls.enable = true;
-          rust_analyzer = {
-            # enable = true;
-            installCargo = false;
-            installRustc = false;
-          };
-        };
-      };
-    };
+    vimAlias = true;
+    viAlias = true;
   };
 }

modules/home/editors/neovim/lazygit.nix

@@ -1,10 +0,0 @@
-{
-  plugins.lazygit.enable = true;
-  keymaps = [
-    {
-      action = "<cmd>LazyGit<CR>";
-      key = "<leader>gg";
-    }
-  ];
-
-}

modules/home/editors/neovim/nvim-tree.nix

@@ -1,13 +0,0 @@
-{
-  plugins.nvim-tree.enable = true;
-  keymaps = [
-    {
-      action = "<cmd>NvimTreeFindFileToggle<CR>";
-      key = "<leader>tt";
-    }
-    {
-      action = "<cmd>NvimTreeFindFile<CR>";
-      key = "<leader>tf";
-    }
-  ];
-}