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/completion.lua

@@ -0,0 +1,55 @@
+-- lua/plugins/completion.lua
+-- Autocompletion via blink.cmp + LuaSnip snippets
+
+return {
+  'saghen/blink.cmp',
+  event = 'VimEnter',
+  version = '1.*',
+  dependencies = {
+    {
+      'L3MON4D3/LuaSnip',
+      version = '2.*',
+      build = (function()
+        -- Regex support in snippets requires a build step.
+        -- Skip on Windows or when make is unavailable.
+        if vim.fn.has 'win32' == 1 or vim.fn.executable 'make' == 0 then
+          return
+        end
+        return 'make install_jsregexp'
+      end)(),
+    },
+    'folke/lazydev.nvim',
+  },
+  --- @module 'blink.cmp'
+  --- @type blink.cmp.Config
+  opts = {
+    keymap = {
+      -- super-tab: Tab to accept, C-n/C-p to navigate
+      preset = 'super-tab',
+    },
+
+    appearance = {
+      nerd_font_variant = 'mono',
+    },
+
+    completion = {
+      documentation = { auto_show = true, auto_show_delay_ms = 300 },
+      menu = {
+        border = 'rounded',
+      },
+    },
+
+    sources = {
+      default = { 'lsp', 'path', 'snippets', 'lazydev' },
+      providers = {
+        lazydev = { module = 'lazydev.integrations.blink', score_offset = 100 },
+      },
+    },
+
+    snippets = { preset = 'luasnip' },
+
+    fuzzy = { implementation = 'lua' },
+
+    signature = { enabled = true, window = { border = 'rounded' } },
+  },
+}