refactor: modularize nvim config into lua/config + lua/plugins

- Extract all options, keymaps, and autocommands into lua/config/
- Move every plugin spec into its own file under lua/plugins/
- Add custom inline orng colorscheme (dark + light) synced to macOS appearance
- Consolidate image.nvim into pdf-viewer.lua (fix duplicate spec)
- Fix image.nvim processor: magick -> magick_cli
- Remove conflicting nvim-autopairs (kept mini.pairs)
- Fix broken <C-f> keymap (was calling non-existent builtin cmd)
- Delete lua/kickstart/ and lua/custom/ folders
- Add colors/orng.vim + colors/orng-light.vim stubs for mid-session switching
- init.lua reduced from 1078 lines to 49 lines

lua/plugins/neo-tree.lua

@@ -0,0 +1,28 @@
+-- lua/plugins/neo-tree.lua
+-- File system explorer
+
+return {
+  'nvim-neo-tree/neo-tree.nvim',
+  version = '*',
+  lazy = false,
+  dependencies = {
+    'nvim-lua/plenary.nvim',
+    'nvim-tree/nvim-web-devicons',
+    'MunifTanjim/nui.nvim',
+  },
+  keys = {
+    { '\\', ':Neotree reveal<CR>', desc = 'NeoTree: reveal current file', silent = true },
+  },
+  opts = {
+    filesystem = {
+      filtered_items = {
+        visible = true, -- show dotfiles
+      },
+      window = {
+        mappings = {
+          ['\\'] = 'close_window',
+        },
+      },
+    },
+  },
+}