fix(maps): measure a booking line along the road before hiding it (#2275)

A short transport hop is hidden once its two ends sit closer than a few
dozen pixels, so a booking that would draw as a dot does not clutter the
map. That check compared the endpoints, which was the whole line while
every hop was straight. A car booking is routed along the road now, and a
road that leaves a town, rounds a lake and comes back to the next town along
can run across half the screen while its ends project sixty pixels apart.
The whole drive vanished until the map was zoomed far enough in for the
ends to separate, which is the gap in the route the report shows.

The decision now walks the line that will actually be drawn, road route or
arcs, and keeps the hop as soon as that reaches the floor. A straight
two-point hop measures exactly what it measured before, so every existing
threshold holds for the case it was written for. One helper serves both
renderers, which also folds the two hand-copied floor tables into it.

client/src/components/Map/MapView.test.tsx

@@ -18,7 +18,13 @@ const mapMock = vi.hoisted(() => ({
   on: vi.fn(),
   off: vi.fn(),
   panBy: vi.fn(),
-  latLngToContainerPoint: vi.fn(() => ({ x: 0, y: 0, distanceTo: () => 1000 })),
+  // A flat projection, 1000 px per degree: far enough apart that every
+  // booking line clears its declutter floor, which is measured along the
+  // projected line (#2275) rather than read off a canned distanceTo.
+  latLngToContainerPoint: vi.fn(([lat, lng]: [number, number]) => ({
+    x: lng * 1000, y: lat * 1000,
+    distanceTo(other: { x: number; y: number }) { return Math.hypot(lng * 1000 - other.x, lat * 1000 - other.y) },
+  })),
   // Panes: jsdom has none, so keep them in a map the pane tests can read back.
   panes: new Map<string, HTMLElement>(),
   getPane: vi.fn(function (this: void, name: string) { return mapMock.panes.get(name) }),