Add daily timezone drift check

tz-drift-check.sh + sky-cam-tzcheck timer notify when TIMEZONE no longer
matches the machine's timezone (timers follow the machine, scripts follow TIMEZONE).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013wi3ZRpfenCe2TRwT4JFMG

install.sh

@@ -296,6 +296,25 @@ for cam in "${CAMERAS[@]}"; do
     fi
 done
 
+# ── Timezone drift check ─────────────────────────────────────────────────────
+# Daily + shortly after boot: notify if TIMEZONE no longer matches the
+# machine's timezone (systemd timers follow the machine, scripts follow TIMEZONE).
+write_service "sky-cam-tzcheck" "timezone drift check" "tz-drift-check.sh"
+cat > "$UNIT_DIR/sky-cam-tzcheck.timer" <<EOF2
+[Unit]
+Description=Sky-Cam — timezone drift check
+
+[Timer]
+OnBootSec=3min
+OnCalendar=*-*-* 12:00:00
+Persistent=true
+
+[Install]
+WantedBy=timers.target
+EOF2
+echo "  wrote sky-cam-tzcheck.timer"
+timers+=("sky-cam-tzcheck")
+
 # ── Generate .env.example ────────────────────────────────────────────────────
 env_example="$HERE/.env.example"
 {