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/extras/fff.lua

@@ -0,0 +1,17 @@
+-- lua/plugins/extras/fff.lua
+-- Fast fuzzy file finder with a native Rust binary
+-- https://github.com/dmtrKovalenko/fff.nvim
+
+return {
+  'dmtrKovalenko/fff.nvim',
+  lazy = false,
+  build = function()
+    require('fff.download').download_or_build_binary()
+  end,
+  opts = {
+    debug = { enabled = false, show_scores = false },
+  },
+  keys = {
+    { 'ff', function() require('fff').find_files() end, desc = 'FFFind files' },
+  },
+}