chore: clean up dotfiles and add gitignore whitelist

Switch to whitelist-based .gitignore to only track essential configs:
nvim, yazi, kitty, zsh, ideavim, karabiner, tmux, scripts, starship.
Remove history, compiled files, and plugin dirs from tracking.

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

nvim/lua/plugins/prettier.lua

@@ -18,7 +18,7 @@ return {
       json            = { "prettier" },
       html            = { "prettier" },
       css             = { "prettier" },
-      markdown        = { "prettier" },
+      markdown        = { "mdformat" },
       yaml            = { "prettier" },
     },
     format_on_save = {