Log an event that happened "now" in one tap

Logging a quick pee/poo/meal/sleep boundary took two taps: open the note
dialog, then Save. Make a single tap on a quick-action log the event
immediately at the current time.

Non-weight quick actions now call addEvent(type, "", Date.now()) directly
and show a brief snackbar with Undo (deletes the just-added event) and Add
note (opens the edit dialog for it), so notes, photos and custom times are
never lost. Weigh-ins still open the dialog since they need a value.
addEvent now returns the created event so the snackbar can reference it.

src/app.js

@@ -258,7 +258,7 @@
   function addEvent(type, note, at, photoId, weight) {
     const events = loadAll();
     const now = Date.now();
-    events.push({
+    const ev = {
       id: uuid(),
       type,
       at: Number.isFinite(at) ? at : now,
@@ -266,10 +266,12 @@
       photoId: photoId || "",
       weight: Number.isFinite(weight) ? weight : undefined,
       updatedAt: now,
-    });
+    };
+    events.push(ev);
     saveAll(events);
     scheduleSync();
     render();
+    return ev;
   }
 
   function updateEvent(id, patch) {
@@ -1602,9 +1604,59 @@
     }
   });
 
+  // ---------- quick-log snackbar ----------
+  // A single tap on a quick-action logs the event at the current instant, then
+  // shows a brief snackbar to undo it or add detail — so the two-tap dialog flow
+  // is never required for a plain pee/poo/meal/sleep boundary. Weigh-ins still
+  // open the dialog since they need a value.
+  const snackbar     = document.getElementById("snackbar");
+  const snackbarMsg  = document.getElementById("snackbar-msg");
+  const snackbarUndo = document.getElementById("snackbar-undo");
+  const snackbarNote = document.getElementById("snackbar-note");
+  let snackbarEvent  = null;
+  let snackbarTimer  = null;
+
+  function hideSnackbar() {
+    clearTimeout(snackbarTimer);
+    snackbarTimer = null;
+    snackbarEvent = null;
+    snackbar.classList.remove("show");
+    snackbar.hidden = true;
+  }
+
+  function showSnackbar(msg, ev) {
+    snackbarEvent = ev;
+    snackbarMsg.textContent = msg;
+    snackbar.hidden = false;
+    void snackbar.offsetWidth; // reflow so the fade-in transition runs
+    snackbar.classList.add("show");
+    clearTimeout(snackbarTimer);
+    snackbarTimer = setTimeout(hideSnackbar, 5000);
+  }
+
+  function quickLog(type) {
+    const ev = addEvent(type, "", Date.now());
+    showSnackbar(`${EVENT_LABELS[type]} logged`, ev);
+  }
+
+  snackbarUndo.addEventListener("click", () => {
+    if (snackbarEvent) deleteEvent(snackbarEvent.id);
+    hideSnackbar();
+  });
+  snackbarNote.addEventListener("click", () => {
+    const ev = snackbarEvent;
+    hideSnackbar();
+    if (ev) openEditDialog(ev);
+  });
+
   // ---------- wiring ----------
   document.querySelectorAll("button.action").forEach(btn => {
-    btn.addEventListener("click", () => openNoteDialog(btn.dataset.type));
+    btn.addEventListener("click", () => {
+      const type = btn.dataset.type;
+      // Weigh-ins need a typed value, so they keep the full dialog.
+      if (type === "weight") { openNoteDialog(type); return; }
+      quickLog(type);
+    });
   });
 
   dayPicker.value = ymd(new Date());