feat(terminal): replace zellij with tmux as terminal multiplexer

Switch from zellij to tmux for terminal multiplexing with mouse support, improved window numbering, and 256-color terminal configuration.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

home.nix

@@ -81,9 +81,9 @@
       if [ -n "$NIX_PROJECT_SHELL" ]; then
         PROMPT="($NIX_PROJECT_SHELL)$PROMPT"
       fi
-      # Only start Zellij if we're in an interactive terminal
-      if [ -z "$ZELLIJ" ] && [ "$TERM" != "linux" ]; then
-        exec zellij
+      # Only start tmux if we're in an interactive terminal
+      if [ -z "$TMUX" ] && [ "$TERM" != "linux" ]; then
+        exec tmux
       fi
     '';
 
@@ -111,16 +111,21 @@
     };
   };
   
-  # Enable zellij (terminal multiplexing)
-  programs.zellij = {
+  # Enable tmux (terminal multiplexing)
+  programs.tmux = {
     enable = true;
 
-    # Optional: write your own config to ~/.config/zellij/config.kdl
-    settings = {
-      theme = "default";
-      pane_frames = true;
-      default_layout = "compact";
-    };
+    # Optional: customize tmux settings
+    extraConfig = ''
+      # Enable mouse support
+      set -g mouse on
+
+      # Start window numbering at 1
+      set -g base-index 1
+
+      # Set terminal colors
+      set -g default-terminal "screen-256color"
+    '';
   };
 
   # Neovim management - using kickstart.nvim via flake