Add bos-update + replicate the dev zsh shell

bos-update: one command that updates both BOS channels — pacman -Syu (snap-pac
snapshotted) and bakery update --all — best-effort so one failing doesn't abort
the other. Baked into the live env and skel.

Shell: match the dev laptop's zsh. Ship Powerlevel10k + zsh-autosuggestions,
zsh-history-substring-search and zsh-syntax-highlighting, sourced from the distro
packages (no oh-my-zsh framework) in the correct order, plus the dev .p10k.zsh.
Powerlevel10k is AUR-only, so it's republished to [breadway] via
packaging/powerlevel10k + a CI workflow (builds libgit2 + gitstatus from source),
same pattern as bibata / zen-browser-bin. skel/.zshrc keeps the BOS QoL aliases
and pywal palette import, with `update` aliased to bos-update.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

iso/airootfs/usr/local/bin/bos-update

@@ -0,0 +1,32 @@
+#!/bin/bash
+# bos-update — update all of BOS in one go.
+#
+# BOS packages come from two channels, so a full update touches both:
+#   1. pacman   — Arch base/desktop + the [breadway] repo (bos-settings, etc.).
+#                 Every transaction is snapshotted by snap-pac, so you can roll
+#                 back from the GRUB "snapshots" submenu or BOS Settings.
+#   2. bakery   — the bread ecosystem apps in ~/.local/bin (bread, breadbar,
+#                 breadbox, breadcrumbs, breadpad, breadman, bread-theme).
+#
+# Best-effort: a failure in one channel doesn't abort the other.
+set -uo pipefail
+
+bold() { printf '\033[1m%s\033[0m\n' "$1"; }
+
+bold "==> System packages (pacman -Syu)"
+if command -v pacman >/dev/null; then
+    sudo pacman -Syu || echo "WARN: pacman update failed"
+else
+    echo "pacman not found; skipping"
+fi
+
+echo
+bold "==> Bread ecosystem (bakery update --all)"
+if command -v bakery >/dev/null; then
+    bakery update --all || echo "WARN: bakery update failed"
+else
+    echo "bakery not found; skipping"
+fi
+
+echo
+bold "==> BOS is up to date."