Make info panels collapsible with remembered state

Each main section with a data-panel key can now be folded by clicking its
heading (rotating chevron, keyboard-accessible via role/tabindex/aria-expanded
and Enter/Space). Collapsed keys are persisted in localStorage and restored on
load, so the layout stays how you left it across reloads.

State is device-global like the theme (a single non-namespaced key, not
per-user data), and only collapsed panels are stored — so any panel added
later defaults to open.

src/app.js

@@ -1765,6 +1765,48 @@
     if (ev) openEditDialog(ev);
   });
 
+  // ---------- collapsible panels ----------
+  // Each main section carrying a data-panel key can be folded by clicking its
+  // heading; collapsed keys are remembered across reloads. State is device-global
+  // (like the theme), so a single non-namespaced key is fine — it's not per-user
+  // data. Only collapsed panels are stored, so newly added panels default open.
+  const PANELS_KEY = "puppy-tracker:panels:v1";
+  function loadPanelState() {
+    try {
+      const s = JSON.parse(localStorage.getItem(PANELS_KEY));
+      return s && typeof s === "object" ? s : {};
+    } catch { return {}; }
+  }
+  function savePanelState(state) {
+    try { localStorage.setItem(PANELS_KEY, JSON.stringify(state)); } catch { /* ignore */ }
+  }
+  function initPanels() {
+    const state = loadPanelState();
+    document.querySelectorAll("main section[data-panel]").forEach(section => {
+      const key = section.dataset.panel;
+      const h2 = section.querySelector(":scope > h2");
+      if (!h2) return;
+      section.classList.add("collapsible");
+      const collapsed = !!state[key];
+      section.classList.toggle("collapsed", collapsed);
+      h2.setAttribute("role", "button");
+      h2.setAttribute("tabindex", "0");
+      h2.setAttribute("aria-expanded", String(!collapsed));
+      const toggle = () => {
+        const nowCollapsed = section.classList.toggle("collapsed");
+        h2.setAttribute("aria-expanded", String(!nowCollapsed));
+        const s = loadPanelState();
+        if (nowCollapsed) s[key] = true; else delete s[key];
+        savePanelState(s);
+      };
+      h2.addEventListener("click", toggle);
+      h2.addEventListener("keydown", (e) => {
+        if (e.key === "Enter" || e.key === " ") { e.preventDefault(); toggle(); }
+      });
+    });
+  }
+  initPanels();
+
   // ---------- wiring ----------
   document.querySelectorAll("button.action").forEach(btn => {
     btn.addEventListener("click", () => {

src/index.html

@@ -97,7 +97,7 @@
         <button type="button" id="day-next" class="ghost" aria-label="Next day">→</button>
       </section>
 
-      <section class="overview">
+      <section class="overview" data-panel="overview">
         <h2 id="overview-title">Today's overview</h2>
         <div class="stats">
           <div class="stat">
@@ -131,7 +131,7 @@
         </div>
       </section>
 
-      <section class="timing">
+      <section class="timing" data-panel="timing">
         <h2>Bathroom timing <span class="muted-note">(last 7 days)</span></h2>
         <div class="lasts">
           <div class="last-row"><span>Typical time between pees</span><span id="gap-pee">—</span></div>
@@ -142,19 +142,19 @@
         <p class="muted-note timing-hint" id="timing-hint"></p>
       </section>
 
-      <section class="sleep">
+      <section class="sleep" data-panel="sleep-windows">
         <h2>Sleep windows</h2>
         <ul id="sleep-list" class="wake-list"></ul>
         <p id="sleep-empty" class="empty">No sleep windows yet for this day.</p>
       </section>
 
-      <section class="wake">
+      <section class="wake" data-panel="wake-windows">
         <h2>Wake windows</h2>
         <ul id="wake-list" class="wake-list"></ul>
         <p id="wake-empty" class="empty">No wake windows yet for this day.</p>
       </section>
 
-      <section class="weekly">
+      <section class="weekly" data-panel="weekly">
         <h2>Last 7 days</h2>
         <div class="chart">
           <div class="chart-title">Sleep (hours)</div>
@@ -183,7 +183,7 @@
         <p class="muted-note">Darker = happens more often at that hour.</p>
       </section>
 
-      <section class="weight">
+      <section class="weight" data-panel="weight">
         <h2>Weight</h2>
         <div class="weight-summary">
           <div class="stat">
@@ -204,7 +204,7 @@
         <p id="weight-empty" class="empty">No weigh-ins logged yet.</p>
       </section>
 
-      <section class="history">
+      <section class="history" data-panel="history">
         <h2>History</h2>
         <ul id="event-list" class="event-list"></ul>
         <p id="empty-state" class="empty">No events logged for this day.</p>

src/style.css

@@ -756,3 +756,24 @@ input.switch:checked::after { transform: translateX(18px); }
 .chart-svg .hm-poo { fill: var(--poo); }
 .chart-svg .hm-eat { fill: var(--eat); }
 
+/* ---------- collapsible panels ---------- */
+section.collapsible > h2 {
+  cursor: pointer;
+  position: relative;
+  padding-right: 20px;
+  -webkit-user-select: none;
+  user-select: none;
+}
+section.collapsible > h2::after {
+  content: "▾";
+  position: absolute;
+  right: 0;
+  top: 50%;
+  transform: translateY(-50%);
+  transition: transform 0.15s ease;
+  color: var(--muted);
+  font-size: 0.85em;
+}
+section.collapsed > h2::after { transform: translateY(-50%) rotate(-90deg); }
+section.collapsed > h2 { margin-bottom: 0; }
+section.collapsed > :not(h2) { display: none; }