Use 1-hour gridlines on the daily Sleep bar chart

niceAxisSleepHours drops from 2-hour to 1-hour steps and is shared with
the trend chart again (the trend-only helper it duplicated is gone).
Labels thin to every other gridline past 12 steps — this chart's plot
area is shorter than the trend's.

src/app.js

@@ -941,12 +941,12 @@
     return { yMax, steps: Math.max(1, Math.round(yMax / step)) };
   }
 
-  // Sleep-specific axis: always 2-hour granularity, capped at 24h/day,
-  // for a more readable picture of typical 10–18 h puppy sleep.
+  // Sleep-specific axis: 1-hour granularity, capped at 24h/day. Shared by the
+  // sleep bars and the trend chart; both thin out labels when steps get dense.
   function niceAxisSleepHours(rawMax) {
     if (!(rawMax > 0)) return { yMax: 2, steps: 2 };
-    const m = Math.min(24, Math.max(2, Math.ceil(rawMax / 2) * 2));
-    return { yMax: m, steps: m / 2 };
+    const m = Math.min(24, Math.max(2, Math.ceil(rawMax)));
+    return { yMax: m, steps: m };
   }
 
   function escapeText(s) {
@@ -980,13 +980,18 @@
     const gap = days.length > 14 ? 2 : 4;
     const barW = (innerW - (days.length - 1) * gap) / days.length;
 
+    // Every gridline gets a label unless that would crowd the 9px text
+    // (this chart's plot area is shorter than the trend chart's).
+    const labelEvery = ySteps > 12 ? 2 : 1;
     const parts = [];
     for (let i = 0; i <= ySteps; i++) {
       const y = MT + innerH * (1 - i / ySteps);
       const v = Math.round(yMax * i / ySteps * 10) / 10;
       const vText = v % 1 === 0 ? v : v.toFixed(1);
       parts.push(`<line class="grid" x1="${ML}" y1="${y}" x2="${W - MR}" y2="${y}"/>`);
-      parts.push(`<text x="${ML - 4}" y="${y + 3}" text-anchor="end">${vText}h</text>`);
+      if (i % labelEvery === 0) {
+        parts.push(`<text x="${ML - 4}" y="${y + 3}" text-anchor="end">${vText}h</text>`);
+      }
     }
 
     const selYmd = ymd(selectedDay());
@@ -1341,14 +1346,6 @@
     return { today, yesterday, avg, avgDays, projected };
   }
 
-  // Trend-specific y-axis: 1-hour gridlines (vs the bar charts' 2-hour steps)
-  // so nearby curves separate visually; still capped at 24h.
-  function niceAxisTrendHours(rawMax) {
-    if (!(rawMax > 0)) return { yMax: 2, steps: 2 };
-    const m = Math.min(24, Math.max(2, Math.ceil(rawMax)));
-    return { yMax: m, steps: m };
-  }
-
   function drawSleepTrendChart(curves) {
     const svg = document.getElementById("chart-sleep-trend");
     if (!svg) return;
@@ -1366,7 +1363,7 @@
     ].filter(s => s.pts && s.pts.length > 1);
 
     const rawMax = Math.max(...series.flatMap(s => s.pts.map(p => p.y)));
-    const { yMax, steps: ySteps } = niceAxisTrendHours(rawMax);
+    const { yMax, steps: ySteps } = niceAxisSleepHours(rawMax);
 
     const xOf = (hour) => ML + (hour / 24) * innerW;
     const yOf = (v) => MT + innerH * (1 - v / yMax);

src/changelog.json

@@ -1,4 +1,5 @@
 [
+  { "date": "2026-07-15", "text": "The Sleep chart in the last-N-days card now has 1-hour gridlines too" },
   { "date": "2026-07-15", "text": "The Sleep trend chart is taller with 1-hour gridlines, so nearby lines are easier to tell apart" },
   { "date": "2026-07-15", "text": "The Sleep trend legend shows the hours for each line — Today, Yesterday and the average, next to the projection" },
   { "date": "2026-07-15", "text": "The Sleep trend chart projects where today will land by midnight — a dashed tail continues today's line following the average day's rhythm" },