Add zsh config: oh-my-zsh + powerlevel10k, lazy-loaded nvm/pyenv

Cuts shell startup from ~440ms to ~150ms by lazy-loading nvm and pyenv
(previously sourced eagerly on every shell start) and caching oh-my-zsh's
completion rescan, which otherwise reran unconditionally every session.
Also fixes a latent bug where oh-my-zsh's extendedglob option silently
broke nvm's default-version auto-activation.

Adds powerlevel10k, zsh-autosuggestions, zsh-syntax-highlighting,
zsh-history-substring-search, zsh-completions, you-should-use, fzf, and
zoxide. install.sh bootstraps a fresh machine: symlinks these dotfiles
and clones the oh-my-zsh theme/plugins.

zsh/.zprofile

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+export PYENV_ROOT="$HOME/.pyenv"
+[[ -d $PYENV_ROOT/bin ]] && export PATH="$PYENV_ROOT/bin:$PATH"
+eval "$(pyenv init --path)"

zsh/.zshenv

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+. "$HOME/.cargo/env"

zsh/.zshrc

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+# Enable Powerlevel10k instant prompt. Must stay close to the top of ~/.zshrc.
+if [[ -r "${XDG_CACHE_HOME:-$HOME/.cache}/p10k-instant-prompt-${(%):-%n}.zsh" ]]; then
+  source "${XDG_CACHE_HOME:-$HOME/.cache}/p10k-instant-prompt-${(%):-%n}.zsh"
+fi
+
+# Add deno completions to search path
+if [[ ":$FPATH:" != *":$HOME/.zsh/completions:"* ]]; then export FPATH="$HOME/.zsh/completions:$FPATH"; fi
+# If you come from bash you might have to change your $PATH.
+# export PATH=$HOME/bin:$HOME/.local/bin:/usr/local/bin:$PATH
+
+# Path to your Oh My Zsh installation.
+export ZSH="$HOME/.oh-my-zsh"
+
+# oh-my-zsh's own compinit call has no caching: it does a full completion
+# rescan (~300ms here) on every single shell start. If we already have a
+# same-day dump, load it the fast way ourselves and turn oh-my-zsh's later
+# call into a no-op. On a stale/missing dump we do nothing here, so
+# oh-my-zsh falls through to its normal (slow but correct) full rebuild.
+# If completions ever look stale after changing `plugins=(...)`, run:
+#   rm -f ~/.zcompdump*; exec zsh
+_zcompdump="${ZDOTDIR:-$HOME}/.zcompdump-${HOST/.*/}-${ZSH_VERSION}"
+if [[ -n ${_zcompdump}(#qN.mh+24) ]]; then
+  autoload -Uz compinit
+  compinit -C -d "$_zcompdump"
+  compinit() { :; }
+fi
+unset _zcompdump
+
+# Set name of the theme to load --- if set to "random", it will
+# load a random theme each time Oh My Zsh is loaded, in which case,
+# to know which specific one was loaded, run: echo $RANDOM_THEME
+# See https://github.com/ohmyzsh/ohmyzsh/wiki/Themes
+ZSH_THEME="powerlevel10k/powerlevel10k"
+
+# Set list of themes to pick from when loading at random
+# Setting this variable when ZSH_THEME=random will cause zsh to load
+# a theme from this variable instead of looking in $ZSH/themes/
+# If set to an empty array, this variable will have no effect.
+# ZSH_THEME_RANDOM_CANDIDATES=( "robbyrussell" "agnoster" )
+
+# Uncomment the following line to use case-sensitive completion.
+# CASE_SENSITIVE="true"
+
+# Uncomment the following line to use hyphen-insensitive completion.
+# Case-sensitive completion must be off. _ and - will be interchangeable.
+# HYPHEN_INSENSITIVE="true"
+
+# Uncomment one of the following lines to change the auto-update behavior
+# zstyle ':omz:update' mode disabled  # disable automatic updates
+# zstyle ':omz:update' mode auto      # update automatically without asking
+# zstyle ':omz:update' mode reminder  # just remind me to update when it's time
+
+# Uncomment the following line to change how often to auto-update (in days).
+# zstyle ':omz:update' frequency 13
+
+# Uncomment the following line if pasting URLs and other text is messed up.
+# DISABLE_MAGIC_FUNCTIONS="true"
+
+# Uncomment the following line to disable colors in ls.
+# DISABLE_LS_COLORS="true"
+
+# Uncomment the following line to disable auto-setting terminal title.
+# DISABLE_AUTO_TITLE="true"
+
+# Uncomment the following line to enable command auto-correction.
+# ENABLE_CORRECTION="true"
+
+# Uncomment the following line to display red dots whilst waiting for completion.
+# You can also set it to another string to have that shown instead of the default red dots.
+# e.g. COMPLETION_WAITING_DOTS="%F{yellow}waiting...%f"
+# Caution: this setting can cause issues with multiline prompts in zsh < 5.7.1 (see #5765)
+# COMPLETION_WAITING_DOTS="true"
+
+# Uncomment the following line if you want to disable marking untracked files
+# under VCS as dirty. This makes repository status check for large repositories
+# much, much faster.
+# DISABLE_UNTRACKED_FILES_DIRTY="true"
+
+# Uncomment the following line if you want to change the command execution time
+# stamp shown in the history command output.
+# You can set one of the optional three formats:
+# "mm/dd/yyyy"|"dd.mm.yyyy"|"yyyy-mm-dd"
+# or set a custom format using the strftime function format specifications,
+# see 'man strftime' for details.
+# HIST_STAMPS="mm/dd/yyyy"
+
+# Would you like to use another custom folder than $ZSH/custom?
+# ZSH_CUSTOM=/path/to/new-custom-folder
+
+# Which plugins would you like to load?
+# Standard plugins can be found in $ZSH/plugins/
+# Custom plugins may be added to $ZSH_CUSTOM/plugins/
+# Example format: plugins=(rails git textmate ruby lighthouse)
+# Add wisely, as too many plugins slow down shell startup.
+plugins=(
+  git sudo extract archlinux docker docker-compose fzf
+  zsh-completions you-should-use
+  zsh-autosuggestions zsh-syntax-highlighting zsh-history-substring-search
+)
+
+source $ZSH/oh-my-zsh.sh
+
+# To customize the prompt, run `p10k configure` or edit ~/.p10k.zsh.
+[[ ! -f ~/.p10k.zsh ]] || source ~/.p10k.zsh
+
+# Up/Down arrows filter history by what's already typed, not just cycle it.
+bindkey '^[[A' history-substring-search-up
+bindkey '^[[B' history-substring-search-down
+
+# zoxide: smarter `cd` that learns frequently/recently used directories.
+command -v zoxide >/dev/null && eval "$(zoxide init zsh)"
+
+# User configuration
+
+# export MANPATH="/usr/local/man:$MANPATH"
+
+# You may need to manually set your language environment
+# export LANG=en_US.UTF-8
+
+# Preferred editor for local and remote sessions
+# if [[ -n $SSH_CONNECTION ]]; then
+#   export EDITOR='vim'
+# else
+#   export EDITOR='nvim'
+# fi
+
+# Compilation flags
+# export ARCHFLAGS="-arch $(uname -m)"
+
+# Set personal aliases, overriding those provided by Oh My Zsh libs,
+# plugins, and themes. Aliases can be placed here, though Oh My Zsh
+# users are encouraged to define aliases within a top-level file in
+# the $ZSH_CUSTOM folder, with .zsh extension. Examples:
+# - $ZSH_CUSTOM/aliases.zsh
+# - $ZSH_CUSTOM/macos.zsh
+# For a full list of active aliases, run `alias`.
+#
+# Example aliases
+# alias zshconfig="mate ~/.zshrc"
+# alias ohmyzsh="mate ~/.oh-my-zsh"
+
+# Lazy-load nvm: sourcing nvm.sh eagerly costs 300-700ms on every shell
+# startup even when node isn't used that session. These stubs load the
+# real nvm on first actual use, then get out of the way.
+export NVM_DIR="$HOME/.nvm"
+_nvm_lazy_load() {
+  unset -f nvm node npm npx corepack
+  # oh-my-zsh sets extendedglob, which breaks nvm's `lts/*`-style alias
+  # globs and silently kills auto-activation of the default version.
+  setopt local_options no_extended_glob
+  [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"
+  [ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"
+}
+nvm() { _nvm_lazy_load; nvm "$@"; }
+node() { _nvm_lazy_load; node "$@"; }
+npm() { _nvm_lazy_load; npm "$@"; }
+npx() { _nvm_lazy_load; npx "$@"; }
+corepack() { _nvm_lazy_load; corepack "$@"; }
+
+# Lazy-load pyenv's shell integration (~130-150ms here). Shims are
+# already on PATH via .zprofile, so `python`/`pip` work immediately
+# without this; it's only needed for `pyenv shell/activate/...` and
+# completions, which this loads for real on first actual `pyenv` call.
+export PYENV_ROOT="$HOME/.pyenv"
+[[ -d $PYENV_ROOT/bin ]] && export PATH="$PYENV_ROOT/bin:$PATH"
+pyenv() {
+  unfunction pyenv
+  eval "$(command pyenv init - zsh)"
+  pyenv "$@"
+}
+
+# bun completions
+[ -s "$HOME/.bun/_bun" ] && source "$HOME/.bun/_bun"
+
+# bun
+export BUN_INSTALL="$HOME/.bun"
+export PATH="$BUN_INSTALL/bin:$PATH"
+
+# pnpm
+export PNPM_HOME="$HOME/.local/share/pnpm"
+case ":$PATH:" in
+  *":$PNPM_HOME/bin:"*) ;;
+  *) export PATH="$PNPM_HOME/bin:$PATH" ;;
+esac
+# pnpm end
+[ -s "$HOME/.deno/env" ] && . "$HOME/.deno/env"