feat(nix): nix and back again

I tried Nix, but it had too many downsides so I removed it.

1. Didn't like that all files are immutable and simple config changes
need a complete rebuild.
2. Setting up a new Mac didn't work as smoothly as promised. Not worth
the effort.
3. It sucked a lot to always have to type in the password twice on each
darwin-rebuild
4. It solves problems I never had.

.config/nvim/lua/plugins/obsidian.lua

@@ -0,0 +1,71 @@
+-- Obsidian
+-- https://github.com/epwalsh/obsidian.nvim
+return {
+  "epwalsh/obsidian.nvim",
+  version = "*",
+  lazy = true,
+  ft = "markdown",
+  dependencies = {
+    -- required
+    "nvim-lua/plenary.nvim",
+    -- optional
+    "hrsh7th/nvim-cmp",
+    "nvim-telescope/telescope.nvim",
+    "ibhagwan/fzf-lua",
+    "junegunn/fzf",
+    "junegunn/fzf.vim",
+    "godlygeek/tabular",
+    "preservim/vim-markdown",
+  },
+  opts = {
+    workspaces = {
+      {
+        name = "zettelkasten",
+        path = "~/Code/GitHub/obsidian/zettelkasten",
+        overrides = {
+          notes_subdir = "pages",
+        },
+      },
+      {
+        name = "highlights",
+        path = "~/Code/GitHub/obsidian/highlights",
+      },
+    },
+    completion = {
+      nvim_cmp = true,
+      min_chars = 2,
+      use_path_only = false,
+    },
+    mappings = {
+      -- Overrides the 'gf' mapping to work on markdown/wiki links within your vault.
+      ["gf"] = {
+        action = function()
+          return require("obsidian").util.gf_passthrough()
+        end,
+        opts = { noremap = false, expr = true, buffer = true },
+      },
+      -- Toggle check-boxes.
+      ["<leader>ch"] = {
+        action = function()
+          return require("obsidian").util.toggle_checkbox()
+        end,
+        opts = { buffer = true },
+      },
+    },
+    disable_frontmatter = true,
+    note_id_func = function(title)
+      local suffix = ""
+      if title ~= nil and title ~= "" then
+        suffix = title
+      else
+        suffix = tostring(os.date("%Y%m%d%H%M"))
+      end
+      return suffix
+    end,
+    templates = {
+      subdir = "templates",
+      date_format = "%Y-%m-%d",
+      time_format = "%H:%M",
+    },
+  },
+}