Add aerial.nvim for document outline

Add aerial.nvim plugin spec with Telescope picker (<leader>O) and
side panel toggle (<leader>o). Extend deploy_nvim in _lib.sh to also
symlink dotfiles/nvim/plugins/ into ~/.config/nvim/lua/plugins/.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

_lib.sh

@@ -79,4 +79,11 @@ deploy_nvim() {
     [[ -f "$mod" ]] || continue
     create_symlink "$mod" ~/.config/nvim/lua/"$(basename "$mod")"
   done
+  if [[ -d "$src_dir/plugins" ]]; then
+    mkdir -p ~/.config/nvim/lua/plugins
+    for mod in "$src_dir/plugins"/*.lua; do
+      [[ -f "$mod" ]] || continue
+      create_symlink "$mod" ~/.config/nvim/lua/plugins/"$(basename "$mod")"
+    done
+  fi
 }

dotfiles/nvim/plugins/aerial.lua

@@ -0,0 +1,25 @@
+return {
+  {
+    "stevearc/aerial.nvim",
+    dependencies = {
+      "nvim-treesitter/nvim-treesitter",
+      "nvim-telescope/telescope.nvim",
+    },
+    keys = {
+      { "<leader>O", "<cmd>Telescope aerial<cr>", desc = "Document outline picker" },
+      { "<leader>o", "<cmd>AerialToggle<cr>",     desc = "Document outline panel" },
+    },
+    config = function()
+      require("aerial").setup({
+        backends = { "treesitter" },
+        show_guides = true,
+        filter_kind = false,
+        layout = {
+          min_width = 20,
+          max_width = { 40, 0.2 },
+        },
+      })
+      require("telescope").load_extension("aerial")
+    end,
+  },
+}