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/which-key.lua

@@ -0,0 +1,29 @@
+-- lua/plugins/which-key.lua
+-- Shows pending keybind completions as you type
+
+return {
+  'folke/which-key.nvim',
+  event = 'VimEnter',
+  opts = {
+    delay = 0,
+    icons = {
+      mappings = vim.g.have_nerd_font,
+      keys = vim.g.have_nerd_font and {} or {
+        Up = '<Up> ', Down = '<Down> ', Left = '<Left> ', Right = '<Right> ',
+        C = '<C-…> ', M = '<M-…> ', D = '<D-…> ', S = '<S-…> ',
+        CR = '<CR> ', Esc = '<Esc> ',
+        ScrollWheelDown = '<ScrollWheelDown> ', ScrollWheelUp = '<ScrollWheelUp> ',
+        NL = '<NL> ', BS = '<BS> ', Space = '<Space> ', Tab = '<Tab> ',
+        F1 = '<F1>', F2 = '<F2>', F3 = '<F3>', F4 = '<F4>',
+        F5 = '<F5>', F6 = '<F6>', F7 = '<F7>', F8 = '<F8>',
+        F9 = '<F9>', F10 = '<F10>', F11 = '<F11>', F12 = '<F12>',
+      },
+    },
+    spec = {
+      { '<leader>s', group = '[S]earch' },
+      { '<leader>t', group = '[T]oggle' },
+      { '<leader>h', group = 'Git [H]unk', mode = { 'n', 'v' } },
+      { '<leader>d', group = '[D]ebug' },
+    },
+  },
+}