Initial Nix configuration setup

- Add nix-darwin and home-manager flake configuration
- Include modular neovim setup with plugins and keybinds
- Add tmux configuration with gruvbox theme and vim-like bindings
- Set up .gitignore for nix build outputs and temporary files

Ready for multi-machine deployment across macOS systems.

.gitignore

@@ -0,0 +1,19 @@
+# Nix build outputs
+result
+result-*
+
+# OS generated files
+.DS_Store
+.DS_Store?
+._*
+.Spotlight-V100
+.Trashes
+ehthumbs.db
+Thumbs.db
+
+# Editor temporary files
+*~
+.#*
+#*#
+*.swp
+*.swo