Stats: fix month-label placement, back to orange

- labels now sit on the week CONTAINING the 1st of the month (old
  logic labelled the first column starting in that month, so a month
  beginning mid-week was labelled a whole column late — hovering the
  cells under 'Aug' showed Jul dates); skip labels that would crowd
  the previous one
- label + grid rows are inline-flex so flexbox shrink can't drift
  them apart at narrow widths
- cell scale back to the orange accent (color-mix of --acc)

static/app.js

@@ -491,15 +491,17 @@ function heatMap(byDay, days) {
   for (const t of ["Mon", "", "Wed", "", "Fri", "", ""]) dcol.append(el("span", null, t));
   const row = el("div", "heat-row");
   row.append(dcol, grid);
-  let lastM = -1;
+  let lastCol = -10, colIdx = 0;  // month label: week containing the 1st
   for (let d = new Date(start); d <= today; ) {
     const col = el("div", "heat-col");
     const lab = el("span", "heat-lab");
-    const labD = new Date(d);
-    for (let i = 0; i < 7 && labD < win; i++) labD.setDate(labD.getDate() + 1);
-    if (labD <= today && labD.getMonth() !== lastM) {
-      lab.textContent = MN[labD.getMonth()];
-      lastM = labD.getMonth();
+    for (let i = 0; i < 7; i++) {
+      const dd = new Date(d); dd.setDate(dd.getDate() + i);
+      if (dd.getDate() === 1 && dd >= win && dd <= today && colIdx - lastCol >= 2) {
+        lab.textContent = MN[dd.getMonth()];
+        lastCol = colIdx;
+        break;  // one label per column, skip if it would crowd the previous
+      }
     }
     lbl.append(lab);
     for (let i = 0; i < 7; i++) {
@@ -518,6 +520,7 @@ function heatMap(byDay, days) {
       col.append(c);
     }
     grid.append(col);
+    colIdx++;
   }
   const lg = el("div", "heat-lg");
   lg.append(el("span", "muted", "less"));