Add activity type and a click-to-open track profile panel

Track properties gain activity_type (FIT: sport enum from the
session/sport message, Garmin's own table; GPX: <trk><type> passed
through as-is) alongside the existing distance/elevation/duration.

Clicking a track line now opens a bottom panel with a chart per
metric the track actually has (elevation always; speed/cadence/heart
rate only when present — FIT's record fields or GPX's device
extensions). TrackStats.build_profile computes cumulative distance
the same way for both formats so they're directly comparable. One
pointermove listener drives a synchronized crosshair across every
chart, a single tooltip listing all series, and a map marker at the
hovered point's position — hovering the chart shows where on the
track that moment was.

public/js/map.js

@@ -8,6 +8,7 @@ import { RadarControl } from "/js/radar.js";
 import { GpxPanelControl } from "/js/gpx.js";
 import { GnssControl } from "/js/gnss.js";
 import { LiveTrackPanelControl } from "/js/livetrack.js";
+import { TrackProfilePanel } from "/js/track_profile.js";
 import { LAYERS_ICON } from "/js/icons.js";
 import { notifySidePanelOpen, onlyOneSidePanelOpen } from "/js/panels.js";
 
@@ -125,7 +126,9 @@ const layerToggle = new LayerToggleControl(applyStyle);
 layerToggle.mount(sidebar);
 layerToggle.setActive("online");
 
-new GpxPanelControl(map).mount(sidebar);
+const profilePanel = new TrackProfilePanel(map);
+profilePanel.mount();
+new GpxPanelControl(map, profilePanel).mount(sidebar);
 new RadarControl(map).mount(sidebar);
 new GnssControl(map).mount(sidebar);
 new LiveTrackPanelControl(map).mount(sidebar);