Update nvim config: switch to tab indentation, update claudecode and vimade settings

Remove stylua.toml (was enforcing 2-space indent), add tab settings in options.lua,
update claudecode.nvim terminal/diff config, lower vimade fadelevel to 0.6, remove
claudecode LazyExtra in favor of custom plugin spec, and add .luarc.json.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nvim/lua/config/options.lua

@@ -1,3 +1,6 @@
 -- Options are automatically loaded before lazy.nvim startup
 -- Default options that are always set: https://github.com/LazyVim/LazyVim/blob/main/lua/lazyvim/config/options.lua
 -- Add any additional options here
+vim.opt.tabstop = 4
+vim.opt.shiftwidth = 4
+vim.opt.softtabstop = 4