Use extId station lookup and clamp walk durations

Add ApiClient.findStationByExtId and toStation helper; use it in
useOriginStationWalk. Clamp OSRM route/step durations to a minimum
walking speed (1.25 m/s) and update tests to mock the new API call.

apps/mobile/src/__tests__/screens.test.tsx

@@ -69,6 +69,12 @@ jest.mock('../hooks/useOriginStationWalk', () => ({
 
 jest.mock('../services/api', () => ({
   api: {
+    findStationByExtId: jest.fn().mockResolvedValue({
+      name: 'Mödling Bahnhof',
+      extId: '1231701',
+      lat: 48.085,
+      lng: 16.296,
+    }),
     searchJourneys: jest.fn().mockResolvedValue([
       {
         id: 'journey-1',

apps/mobile/src/hooks/useOriginStationWalk.ts

@@ -24,9 +24,9 @@ export function useOriginStationWalk(origin: Station | null) {
       if (origin?.lat == null || origin.lng == null) return;
 
       try {
-        const nearest = await api.findNearestStationByCoords(origin.lat, origin.lng);
+        const selectedStation = await api.findStationByExtId(origin.extId);
         if (!isMounted) return;
-        setStation(nearest);
+        setStation(selectedStation);
       } catch (err) {
         if (!isMounted) return;
         setLookupError(err instanceof Error ? err.message : 'Origin station lookup failed');

apps/web/src/lib/walk-routing-client.ts

@@ -2,6 +2,8 @@ import type { WalkRoute, WalkStep } from "@timetoleave/core";
 import { OSRM_URL } from "./constants";
 import { ApiClient } from "./api-service";
 
+const WALKING_METERS_PER_SECOND = 1.25;
+
 // ---------------------------------------------------------------------------
 // OSRM response types (internal, not exported)
 // ---------------------------------------------------------------------------
@@ -76,16 +78,17 @@ export class WalkRoutingClient {
       if (res.code !== "Ok" || !res.routes.length) return null;
 
       const route = res.routes[0];
+      const walkingDuration = Math.ceil(route.distance / WALKING_METERS_PER_SECOND);
       const steps: WalkStep[] = (route.legs[0]?.steps ?? []).map((s) => ({
         name: s.name,
         distance: s.distance,
-        duration: s.duration,
+        duration: Math.max(s.duration, Math.ceil(s.distance / WALKING_METERS_PER_SECOND)),
         instruction: stepInstruction(s),
       }));
 
       return {
         distance: route.distance,
-        duration: route.duration,
+        duration: Math.max(route.duration, walkingDuration),
         steps,
       };
     }