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/config/autocmds.lua

@@ -0,0 +1,11 @@
+-- lua/config/autocmds.lua
+-- Global autocommands
+
+-- Highlight yanked text briefly
+vim.api.nvim_create_autocmd('TextYankPost', {
+  desc = 'Highlight when yanking (copying) text',
+  group = vim.api.nvim_create_augroup('user-highlight-yank', { clear = true }),
+  callback = function()
+    vim.hl.on_yank()
+  end,
+})