Bug: Path Between Destinations Does Not Follow Roads

[kirillakovalenko]

Description

On the Results page, route polylines are drawn as straight lines connecting each stop
in sequence instead of following the actual road network (streets, turns, one-ways).
This misrepresents the real driving path and makes the on-map distance/route look
nothing like what a driver would actually drive.

The map already intends to draw road-following routes: RoutePolylinesOverlay calls
Google's DirectionsService and only draws a straight polyline as a fallback
(drawFallback, app/ui/src/app/results/components/Map.tsx#L140-L150). In practice every route renders as the fallback,
which means the directions request is either failing, returning no overview_path, or
being skipped. Likely causes to check:

• Directions API not enabled / not authorized for the Maps API key
  (NEXT_PUBLIC_GOOGLE_MAPS_KEY) — the catch at L224-L230 logs
  "DirectionsService failed, falling back to straight line".
• Routes with more than 25 waypoints hit the hard fallback at L163-L166.
• result.routes[0].overview_path empty/missing → fallback at L196-L200.

Goal

Route polylines on the Results page follow the real road network between consecutive
stops instead of drawing straight lines.

Reproduction

Steps

1. From a clean state, build a route (add addresses + a vehicle) and run Optimize.
2. Open the Results page.
3. Observe the route line connecting the depot and each stop on the map.

Expected: The polyline follows the drivable roads and turns between each stop,
matching the path a driver would take.
Actual: The polyline is a straight line directly between each consecutive stop.

Environment: branch main. Check the browser console for the
"DirectionsService failed, falling back to straight line" warning, and confirm whether
the Maps key has the Directions API enabled.

Scope

In scope

• Diagnose why DirectionsService results aren't being used and ensure road-following
  polylines render for normal routes on the Results page.
• Confirm the Directions API is enabled/authorized for the configured Maps key (or
  document the required config).

Out of scope

• Routes exceeding the 25-waypoint Directions limit (the straight-line fallback there
  is acceptable for now; splitting into multiple legs is a separate follow-up).
• Changing the optimization/solver output or stop ordering.
• The mobile app and driver-view map.

Acceptance Criteria

• After running the reproduction steps, the route polyline follows roads/turns
  rather than a straight line.
• No "DirectionsService failed" warning in the console for a normal (<25 stop) route.
• On-map route distance reflects the road path (via onRouteDistanceUpdate), not
  straight-line distance.
• Straight-line fallback still triggers only when directions are genuinely
  unavailable, and does not throw.

Assignee

@KesarSidhu