Reconcile cross-platform fixes and resolve review comments

[Copilot]

Consolidates changes from PR #2 (cross-platform reliability fixes) and addresses 3 unresolved review comments.

Review comment fixes

Bootstrap/stow.sh: Compute uname -s once before loop instead of per-iteration

local os=$(uname -s)
for dir in */; do
    if [[ "$os" != "Darwin" ]]; then
        # ...

Zsh/.zprofile: Re-add EDITOR/VISUAL exports for non-interactive login shells

export EDITOR='vim'
export VISUAL="$EDITOR"

.shell_common will override these with nvim when sourced by interactive shells.

README.md: Update platform description to reflect that .zshrc is now cross-platform, not macOS-only.

Included from PR #2

• Cross-platform Homebrew detection (Apple Silicon + Intel)
• Move .shell_common sourcing before modern CLI tools in .zshrc
• BSD-compatible du flags (-d 1 vs --max-depth=1)
• zipr function with argument validation
• Git aliases: push.default = simple, discard = restore --
• Skip macOS-only packages on Linux in bootstrap

Original prompt

Pull Request: #2

There are two open prs in this repo. I want to reconcile both into one and fix all of copilot's unresolved comments.

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[Copilot]

Pull request overview

This PR reconciles cross-platform reliability fixes from PR #2 and addresses 3 unresolved review comments to improve shell configuration portability and bootstrap script efficiency.

Changes:

• Re-add EDITOR/VISUAL exports to .zprofile for non-interactive login shells (vim as default, overridden by .shell_common for interactive shells with nvim detection)
• Optimize bootstrap script by computing uname -s once before loop instead of per-iteration
• Clarify README platform description to reflect that .zshrc is cross-platform, not macOS-only

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
Zsh/.zprofile	Re-adds EDITOR/VISUAL exports for non-interactive login shells
Bootstrap/stow.sh	Optimizes uname call by computing once before loop
README.md	Updates platform description to clarify .zshrc is cross-platform

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