Label each risk-trend point with its risk, not the scan id

The bubble at each point on the risk trend now shows that scan's risk number,
so the line can be read straight off without tracing back to the axis.  The
scan it belongs to is still the link behind the point and is still named in its
hover title, so nothing is lost in telling the scans apart.

Author: hackrange

app/core/charts.py

@@ -217,7 +217,10 @@ def y_at(value):
     marks = []
     for i, point in enumerate(points):
         x, y = x_at(i), y_at(values[i])
-        label = str(point.get("id") or "")
+        # The bubble shows the risk value itself, so the trend reads without
+        # tracing back to the axis; the scan it belongs to is still the link
+        # and is named in the point's hover title.
+        label = str(values[i])
         bubble_w = round(len(label) * 6.6 + 12, 1)
         # Centre the bubble on the point, then keep it inside the frame so the
         # first and last ones are not clipped at the edges.

app/web/templates/external_site.html

@@ -266,7 +266,7 @@
           </div>
         </div>
         {% endfor %}
-        <div class="faint small risk-trend-note">Each point is one finished scan, oldest on the left.  Risk weighs findings by severity: critical 25, high 12, medium 5, low 2.  The number in each bubble is the scan id; click a point to open that scan.  A dot takes the color of the scan's worst finding.</div>
+        <div class="faint small risk-trend-note">Each point is one finished scan, oldest on the left.  Risk weighs findings by severity: critical 25, high 12, medium 5, low 2.  The number in each bubble is that scan's risk; click a point to open the scan behind it.  A dot takes the color of the scan's worst finding.</div>
       </div>
       {% else %}<div class="empty">No finished scan yet, so there is nothing to trend.</div>{% endif %}
     </div>