Add copy mode indicator styling with bright purple theme

- Add mode-style with bright purple background (#d3869b) matching prefix indicator
- Style search matches with yellow and current match with red
- Add [COPY] indicator to status bar when in copy mode
- Provides consistent visual feedback across tmux modes

Copy mode now shows:
- Bright purple position indicator in pane
- [COPY] text in status bar alongside time
- Themed search highlighting for better visibility

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

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

modules/tmux.nix

@@ -33,11 +33,16 @@
       set -g message-style 'bg=#fabd2f,fg=#282828'
       set -g message-command-style 'bg=#fabd2f,fg=#282828'
       
+      # Copy mode colors
+      set -g mode-style 'bg=#d3869b,fg=#282828'
+      set -g copy-mode-match-style 'bg=#fabd2f,fg=#282828'
+      set -g copy-mode-current-match-style 'bg=#fb4934,fg=#282828'
+      
       # Status bar content
       set -g status-left-length 40
       set -g status-right-length 30
       set -g status-left '#{?client_prefix,#[bg=#d3869b],#[bg=#a89984]}#[fg=#282828] #S #[default]'
-      set -g status-right ' %H:%M '
+      set -g status-right '#{?pane_in_mode,[COPY],} %H:%M '
       
       # Window status format
       set -g window-status-format ' #I:#W '