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/conform.lua

@@ -0,0 +1,50 @@
+-- lua/plugins/conform.lua
+-- Code formatting via conform.nvim
+
+return {
+  'stevearc/conform.nvim',
+  event = { 'BufWritePre' },
+  cmd = { 'ConformInfo' },
+  keys = {
+    {
+      '<leader>f',
+      function()
+        require('conform').format { async = true, lsp_format = 'fallback' }
+      end,
+      mode = '',
+      desc = '[F]ormat buffer',
+    },
+  },
+  opts = {
+    notify_on_error = false,
+
+    format_on_save = function(bufnr)
+      -- Disable lsp_fallback for languages without a standardized style.
+      local disable_filetypes = { c = true, cpp = true }
+      if disable_filetypes[vim.bo[bufnr].filetype] then
+        return nil
+      end
+      return { timeout_ms = 500, lsp_format = 'fallback' }
+    end,
+
+    formatters = {
+      yamlfmt = {
+        prepend_args = { '-conf', vim.fn.expand '~/.config/yamlfmt/.yamlfmt' },
+      },
+    },
+
+    formatters_by_ft = {
+      lua        = { 'stylua' },
+      python     = { 'black' },
+      javascript      = { 'biome', 'prettier', stop_after_first = true },
+      typescript      = { 'biome', 'prettier', stop_after_first = true },
+      javascriptreact = { 'biome', 'prettier', stop_after_first = true },
+      typescriptreact = { 'biome', 'prettier', stop_after_first = true },
+      json       = { 'biome', 'prettier', stop_after_first = true },
+      html       = { 'prettier' },
+      css        = { 'prettier' },
+      graphql    = { 'prettier' },
+      yaml       = { 'yamlfmt' },
+    },
+  },
+}