Label the revenue axis in euros

The y-axis ticks and the hover both carry the unit now — an axis in euros with a
bare number in the tooltip reads as two different quantities.

Two formatters, not one: the axis rounds to whole euros to keep the labels short,
but the tooltip keeps the cents. Rounding an amount someone is reading off a
chart to answer "how much did we take in March" is a lie, and €1.234,50 becoming
"€ 1.235" is exactly that.

Locale is nl-BE, so it renders "€ 1.234,50" rather than "€1,234.5".

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

static/css/app.css

@@ -3357,6 +3357,9 @@
   .overflow-x-auto {
     overflow-x: auto;
   }
+  .rounded {
+    border-radius: 0.25rem;
+  }
   .rounded-box {
     border-radius: var(--radius-box);
   }