Refuse to run the Linux setup as root

setup-linux.sh accepted being run as root and simply set SUDO="". That quietly
broke everything user-scoped: PM2 keeps its process list in $HOME/.pm2 and the
login entry goes in $HOME/.config/autostart, so under sudo both landed in /root.
The install reported success, then `pm2 list` as the real user showed nothing -
it was talking to a different daemon - and the autostart entry sat in a home
directory that never logs in.

Both scripts now refuse, and name the account to use when SUDO_USER says how
they were invoked. setup-linux.sh still uses sudo for apt, which is the only
part that needs it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/install-autostart.sh

@@ -31,6 +31,16 @@ done
 info() { printf '  %s\n' "$1"; }
 warn() { printf '  ! %s\n' "$1" >&2; }
 
+# Same reason as setup-linux.sh: PM2's process list lives in $HOME/.pm2 and the
+# login entry in $HOME/.config/autostart. As root both go to /root, invisible to
+# the account that actually logs in.
+if [ "$(id -u)" -eq 0 ]; then
+    echo "  [X] do not run this as root${SUDO_USER:+ - run it as $SUDO_USER}." >&2
+    echo "      PM2 and the login entry are per-user; as root they land in /root" >&2
+    echo "      and your own 'pm2 list' will be empty." >&2
+    exit 1
+fi
+
 info "project root: $ROOT"
 
 # ── PM2 ─────────────────────────────────────────────────────────────────────

setup-linux.sh

@@ -29,12 +29,20 @@ echo
 
 # ── sudo ────────────────────────────────────────────────────────────────────
 command -v apt-get >/dev/null 2>&1 || die "this script expects apt (Raspberry Pi OS, Debian, Ubuntu)"
-SUDO=""
-if [ "$(id -u)" -ne 0 ]; then
-    command -v sudo >/dev/null 2>&1 || die "not root and sudo is not installed"
-    SUDO="sudo"
-    info "some steps need sudo; you may be prompted"
+# Must NOT run as root. Almost everything here is user-scoped: PM2 keeps its
+# process list in $HOME/.pm2, and the login entry goes in $HOME/.config/autostart.
+# Run under sudo and both land in /root - PM2 starts a daemon your own account
+# cannot see, and the autostart entry sits in a home directory that never logs
+# in. It looks like it worked, then `pm2 list` is empty.
+if [ "$(id -u)" -eq 0 ]; then
+    if [ -n "${SUDO_USER:-}" ]; then
+        die "do not run this with sudo - run it as $SUDO_USER; it will ask for sudo only where it needs it"
+    fi
+    die "do not run this as root - run it as the user that will own the instance"
 fi
+command -v sudo >/dev/null 2>&1 || die "sudo is required (for apt) and is not installed"
+SUDO="sudo"
+info "apt steps need sudo; you may be prompted"
 
 # ── system packages ─────────────────────────────────────────────────────────
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