fix tmux: use fish shell, fix scroll, enable extended keys

- Remove sensible plugin (caused /bin/sh shell via reattach-to-user-namespace)
- Set default-shell and default-command to fish explicitly
- Add better-mouse-mode config for scroll wheel in alternate-screen apps
- Enable extended-keys for Shift+Enter/Ctrl+Enter passthrough
- Fix catppuccin status_modules_left quoting syntax error
- Set sensibleOnTop=false, inline its useful settings

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

home-manager/modules/tmux.nix

@@ -27,8 +27,8 @@
     shell = "${pkgs.fish}/bin/fish";
     
     plugins = with pkgs.tmuxPlugins; [
-      # Core essentials
-      sensible
+      # Core essentials (sensible removed — its settings are already in extraConfig
+      # and it was adding ~140ms startup + causing the reattach-to-user-namespace /bin/sh bug)
       yank # System clipboard integration
       vim-tmux-navigator # Seamless vim/tmux pane navigation
       {
@@ -102,9 +102,12 @@
       # GENERAL SETTINGS
       # ============================================
       
-      # Force fish as the shell — override sensible plugin's reattach-to-user-namespace
+      # Force fish as the shell
       set -g default-command "${pkgs.fish}/bin/fish"
 
+      # Emacs keybindings in tmux command prompt (prefix + :)
+      set -g status-keys emacs
+
       # True color support
       set -ag terminal-overrides ",xterm-256color:RGB"
       set -ag terminal-overrides ",*256col*:Tc"