Add comprehensive zsh configuration with Powerlevel10k

- Create separate zsh.nix module for enhanced shell experience
- Add Powerlevel10k theme with custom configuration from wizard
- Include useful aliases for git, nix, and navigation commands
- Add modern CLI tools: fzf, fd, ripgrep, bat for better productivity
- Enable autosuggestions, syntax highlighting, and completion
- Add portable p10k.zsh configuration for consistent prompt across machines
- Update flake.nix to import zsh module and remove inline config
- Update tmux.nix with prefix indicator and datetime removal

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

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

tmux.nix

@@ -35,9 +35,9 @@
       
       # Status bar content
       set -g status-left-length 40
-      set -g status-right-length 50
+      set -g status-right-length 20
       set -g status-left ' #S '
-      set -g status-right ' %H:%M %d-%b-%y '
+      set -g status-right '#{?client_prefix,#[reverse]<Prefix>#[noreverse] ,}'
       
       # Window status format
       set -g window-status-format ' #I:#W '