Stats: fix month-label alignment on the heatmap

Label slots were 14px wide + 3px gap (17px pitch) vs grid columns
11px + 3px gap (14px pitch), so labels drifted up to ~150px right of
their column by the last month. Label slots are now exactly cell
width with min-width: 0 so the text overflows instead of widening
the slot.

static/style.css

@@ -58,8 +58,9 @@ h2 { margin: 0.4rem 0; }
 .stat-value { font-size: 1.3rem; font-weight: 700; }
 .heat-wrap { overflow-x: auto; margin: .5rem 0 .3rem; background: var(--card);
   border: 1px solid var(--bd); border-radius: 10px; padding: .7rem .8rem .5rem; }
-.heat-lbl { display: flex; gap: 3px; margin-bottom: 2px; }
-.heat-lbl .heat-lab { width: 14px; font-size: .65rem; color: var(--muted); white-space: nowrap; }
+.heat-lbl { display: flex; gap: 3px; margin-bottom: 2px; height: 12px; }
+.heat-lbl .heat-lab { width: 11px; min-width: 0; font-size: .65rem;
+  color: var(--muted); white-space: nowrap; }
 .heat { display: flex; gap: 3px; }
 .heat-col { display: flex; flex-direction: column; gap: 3px; }
 .heat i, .heat-lg i { width: 11px; height: 11px; border-radius: 2px; background: var(--bd); }