docs+test: ecosystem matrix, keybinds, limitations, recovery, smoke test

README: add a bread-ecosystem feature matrix, keyboard-shortcut reference,
a Known Limitations section (NVIDIA/Mesa, VM GPU accel, Secure Boot, btrfs
assumption), and a Recovery guide (snapshot rollback + GRUB/EFI repair from
the live ISO).

scripts/smoke-test.sh: read-only post-install validator — btrfs subvolumes,
snapper config, enabled services, bread bins on PATH, bos-settings, default
dotfiles, and the GRUB EFI artifacts. Exits non-zero on any failure.

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

scripts/smoke-test.sh

@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+# BOS post-install smoke test.
+#
+# Run this INSIDE a freshly installed BOS (as the main user) to assert the
+# install's core invariants. It is read-only and safe to run any time.
+#
+#   ./smoke-test.sh
+#
+# Exit status is non-zero if any check fails, so it can gate CI / manual QA.
+set -uo pipefail
+
+pass=0 fail=0
+ok()   { printf '  \033[32mPASS\033[0m  %s\n' "$1"; pass=$((pass+1)); }
+bad()  { printf '  \033[31mFAIL\033[0m  %s\n' "$1"; fail=$((fail+1)); }
+note() { printf '  \033[33m----\033[0m  %s\n' "$1"; }
+
+check() { if eval "$2" >/dev/null 2>&1; then ok "$1"; else bad "$1"; fi; }
+
+echo "== btrfs subvolume layout =="
+if command -v btrfs >/dev/null; then
+    # `btrfs subvolume list` needs root; try unprivileged, fall back to non-
+    # interactive sudo (no hang if creds aren't cached).
+    paths="$(btrfs subvolume list / 2>/dev/null || sudo -n btrfs subvolume list / 2>/dev/null)"
+    paths="$(awk '{print $NF}' <<<"$paths")"
+    if [ -z "$paths" ]; then
+        note "couldn't list subvolumes (need root) — skipping"
+    else
+        for sv in @ @home @snapshots @log @cache; do
+            if grep -qx "$sv" <<<"$paths"; then ok "subvolume $sv present"; else bad "subvolume $sv missing"; fi
+        done
+    fi
+else
+    note "btrfs not installed (not a btrfs root?) — skipping subvolume checks"
+fi
+
+echo "== snapshot tooling =="
+check "snapper root config exists" "[ -f /etc/snapper/configs/root ]"
+check "snap-pac hook present"      "pacman -Qq snap-pac"
+check "grub-btrfs present"         "pacman -Qq grub-btrfs"
+
+echo "== enabled system services =="
+for unit in NetworkManager.service greetd.service bluetooth.service tlp.service \
+            cups.socket avahi-daemon.service ufw.service systemd-timesyncd.service; do
+    check "$unit enabled" "systemctl is-enabled $unit"
+done
+check "graphical.target is default" "[ \"\$(systemctl get-default)\" = graphical.target ]"
+
+echo "== bread ecosystem on PATH =="
+for bin in bakery bread breadd breadbar breadbox breadbox-sync breadcrumbs breadpad breadman; do
+    check "$bin found" "command -v $bin"
+done
+
+echo "== bos-settings =="
+check "bos-settings installed" "command -v bos-settings"
+
+echo "== default dotfiles =="
+check "hyprland.lua present"  "[ -f \"\$HOME/.config/hypr/hyprland.lua\" ]"
+check "mimeapps.list present" "[ -f \"\$HOME/.config/mimeapps.list\" ]"
+check "kitty config present"  "[ -f \"\$HOME/.config/kitty/kitty.conf\" ]"
+
+echo "== bootloader (EFI) =="
+check "GRUB EFI binary present" \
+    "[ -f /boot/efi/EFI/BOS/grubx64.efi ] || [ -f /boot/efi/EFI/BOOT/BOOTX64.EFI ]"
+check "grub.cfg present" "[ -f /boot/grub/grub.cfg ]"
+
+echo
+printf 'Result: \033[32m%d passed\033[0m, \033[31m%d failed\033[0m\n' "$pass" "$fail"
+[ "$fail" -eq 0 ]