Tweaks: Zsh Startup Time (2.5s -> 0.08s)

Problem: Every new terminal and tmux pane took ~2.5 seconds to show the prompt. With 100–200 windows/panes opened per day in my terminal-native workflow, that's 4–8 minutes of waiting daily. I'd tolerated it because my .zshrc hadn't been meaningfully touched since 2010 and I wasn't eager to dive into that project.