implemented aligned notes

src/diagram.typ

@@ -58,6 +58,7 @@
   // List participants
   let linked = ()
   let last-seq = none
+  let last-note = none
   for (i, elmt) in elmts.enumerate() {
     if elmt.type == "par" {
       participants.push(elmt)
@@ -107,12 +108,21 @@
         seq.insert("linked-note", elmt)
         elmts.at(last-seq.i) = seq
       }
+      if elmt.aligned {
+        let n = last-note.elmt
+        n.aligned-with = elmt
+        elmts.at(last-note.i) = n
+      }
       elmts.at(i) = elmt
       if elmt.side == "left" {
         linked.push("[")
       } else if elmt.side == "right" {
         linked.push("]")
       }
+      last-note = (
+        elmt: elmt,
+        i: i
+      )
     }
   }
   linked = linked.dedup()