Update to (somewhat?) dendritic pattern

Heavily inspired by https://github.com/Doc-Steve/dendritic-design-with-flake-parts.

> Atomic commits? Never heard of them!

modules/programs/nixvim/_nixvim-config/options.nix

@@ -0,0 +1,50 @@
+{ ... }: {
+  opts = {
+    # Expand tabs to 4 spaces
+    shiftwidth = 4;
+    softtabstop = 4;
+    expandtab = true;
+
+    signcolumn = "yes:3";
+
+    # automatically indent and try to be smart about it
+    autoindent = true;
+    smartindent = true;
+
+    # Relative line numbers
+    number = true;
+    relativenumber = true;
+
+    # See search result as you type
+    inccommand = "split";
+
+    # Visualize whitespace
+    list = true;
+    listchars = {
+      tab = "» ";
+      trail = "·";
+      nbsp = "␣";
+    };
+
+    # Show which line the cursor is on
+    cursorline = true;
+
+    # Keep the cursor somewhat centered on the screen
+    scrolloff = 25;
+
+    # Ask if operations would fail due to unsaved buffers
+    confirm = true;
+
+    # ignore case in search unless multiple capital case letter have been typed
+    smartcase = true;
+    ignorecase = true;
+
+    completeopt = "menu,menuone,noselect";
+
+    # Persistent undos :)
+    undofile = true;
+
+    # enable resize by mouse
+    mouse = "n";
+  };
+}