feat: replace zellij with tmux for terminal multiplexing

Switch from zellij to tmux with vi keybindings, mouse support, and custom prefix (Ctrl-a). Updates auto-start logic in zsh to launch tmux instead of zellij.

🤖 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
     '';
 
@@ -102,16 +102,31 @@
     };
   };
   
-  # 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";
-    };
+    # Basic tmux configuration
+    terminal = "screen-256color";
+    historyLimit = 10000;
+    keyMode = "vi";
+    mouse = true;
+
+    extraConfig = ''
+      # Set prefix to Ctrl-a instead of Ctrl-b
+      unbind C-b
+      set-option -g prefix C-a
+      bind-key C-a send-prefix
+
+      # Split panes using | and -
+      bind | split-window -h
+      bind - split-window -v
+      unbind '"'
+      unbind %
+
+      # Reload config file
+      bind r source-file ~/.config/tmux/tmux.conf
+    '';
   };
 
   # Neovim management