Make the Sleep trend chart taller with a finer 1-hour y-axis

220px viewBox (was 160) and 1-hour gridlines via a trend-specific axis
helper, so curves that run close together separate visually. Labels
drop to every other gridline past 16 steps to keep the text readable.

src/app.js

@@ -1341,10 +1341,18 @@
     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;
-    const W = 320, H = 160;
+    const W = 320, H = 220;
     const ML = 26, MR = 8, MT = 10, MB = 22;
     const innerW = W - ML - MR;
     const innerH = H - MT - MB;
@@ -1358,18 +1366,22 @@
     ].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 } = niceAxisSleepHours(rawMax);
+    const { yMax, steps: ySteps } = niceAxisTrendHours(rawMax);
 
     const xOf = (hour) => ML + (hour / 24) * innerW;
     const yOf = (v) => MT + innerH * (1 - v / yMax);
 
+    // Every gridline gets a label unless that would crowd the 9px text.
+    const labelEvery = ySteps > 16 ? 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>`);
+      }
     }
     for (const hr of [0, 6, 12, 18, 24]) {
       const x = xOf(hr);