Show Eurostar Standard prices and total journey cost on results page

Fetches prices via the site-api.eurostar.com GraphQL gateway
(NewBookingSearch operation, discovered with Playwright). Adds
fetch_prices() to scraper/eurostar.py using requests, caches results,
annotates each trip with eurostar_price and total_price, and shows an
ES Std column plus total cost (duration + price) in the results table.
The Transfer column is hidden on small screens for mobile usability.

Closes #4

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scraper/eurostar.py

@@ -1,7 +1,7 @@
 """
-Scrape Eurostar timetable via httpx.
+Scrape Eurostar timetable via httpx and fetch prices via the GraphQL API.
 
-The route-specific timetable pages are Next.js SSR — all departure data is
+Timetable: route-specific pages are Next.js SSR — all departure data is
 embedded in <script id="__NEXT_DATA__"> as JSON, so no browser / JS needed.
 
 URL pattern:
@@ -12,10 +12,19 @@ Data path: props.pageProps.pageData.liveDepartures[]
   .origin.model.scheduledDepartureDateTime  → London departure
   .destination.model.scheduledArrivalDateTime → destination arrival
     (already filtered to the requested stop, not the final stop)
+
+Prices: POST https://site-api.eurostar.com/gateway (GraphQL, operationName
+NewBookingSearch).  The `journeys[].fares[]` array contains one entry per
+class of service; we extract the Eurostar Standard (classOfService.code ==
+"STANDARD") displayPrice for 1 adult, in GBP.
 """
 import json
+import random
 import re
+import string
+
 import httpx
+import requests
 
 DEFAULT_UA = (
     "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 "
@@ -90,3 +99,105 @@ def fetch(destination: str, travel_date: str,
         r = client.get(url, params={'date': travel_date})
     r.raise_for_status()
     return _parse(r.text, destination)
+
+
+# ---------------------------------------------------------------------------
+# Price fetching via site-api.eurostar.com GraphQL
+# ---------------------------------------------------------------------------
+
+_GATEWAY_URL = 'https://site-api.eurostar.com/gateway'
+
+# Minimal query requesting only timing + Eurostar Standard fare price.
+# Variable names and inline argument names match what the site sends so the
+# server-side query planner sees a familiar shape.
+_GQL_PRICES = (
+    "query NewBookingSearch("
+    "$origin:String!,$destination:String!,$outbound:String!,"
+    "$currency:Currency!,$adult:Int,"
+    "$filteredClassesOfService:[ClassOfServiceEnum]"
+    "){"
+    "journeySearch("
+    "outboundDate:$outbound origin:$origin destination:$destination"
+    " adults:$adult currency:$currency"
+    " productFamilies:[\"PUB\"] contractCode:\"EIL_ALL\""
+    " adults16Plus:0 children:0 youths:0 children4Only:0 children5To11:0"
+    " infants:0 adultsWheelchair:0 childrenWheelchair:0 guideDogs:0"
+    " wheelchairCompanions:0 nonWheelchairCompanions:0"
+    " isAftersales:false multipleFlexibility:true showAllSummatedFares:false"
+    " seniorsAges:[] prioritiseShortHaulODTrains:true"
+    "){"
+    "outbound{"
+    "journeys("
+    "hideIndirectTrainsWhenDisruptedAndCancelled:false"
+    " hideDepartedTrains:true"
+    " hideExternalCarrierTrains:true"
+    " hideDirectExternalCarrierTrains:true"
+    "){"
+    "timing{departureTime:departs __typename}"
+    "fares(filteredClassesOfService:$filteredClassesOfService){"
+    "classOfService{code __typename}"
+    "prices{displayPrice __typename}"
+    "seats __typename"
+    "}"
+    "__typename"
+    "}"
+    "__typename"
+    "}"
+    "__typename"
+    "}"
+    "}"
+)
+
+
+def _generate_cid() -> str:
+    chars = string.ascii_letters + string.digits
+    return 'SRCH-' + ''.join(random.choices(chars, k=22))
+
+
+def fetch_prices(destination: str, travel_date: str) -> dict[str, int | None]:
+    """
+    Return Eurostar Standard prices for every departure on travel_date.
+
+    Result: {depart_st_pancras: price_gbp_int_or_None}
+    None means the class is sold out or unavailable for that departure.
+    """
+    dest_id = DESTINATION_STATION_IDS[destination]
+    headers = {
+        'User-Agent': DEFAULT_UA,
+        'Content-Type': 'application/json',
+        'Accept': '*/*',
+        'Accept-Language': 'en-GB',
+        'Referer': 'https://www.eurostar.com/',
+        'x-platform': 'web',
+        'x-market-code': 'uk',
+        'x-source-url': 'search-app/',
+        'cid': _generate_cid(),
+    }
+    payload = {
+        'operationName': 'NewBookingSearch',
+        'variables': {
+            'origin': ORIGIN_STATION_ID,
+            'destination': dest_id,
+            'outbound': travel_date,
+            'currency': 'GBP',
+            'adult': 1,
+            'filteredClassesOfService': ['STANDARD'],
+        },
+        'query': _GQL_PRICES,
+    }
+    resp = requests.post(_GATEWAY_URL, json=payload, headers=headers, timeout=20)
+    resp.raise_for_status()
+    data = resp.json()
+    prices: dict[str, int | None] = {}
+    journeys = data['data']['journeySearch']['outbound']['journeys']
+    for journey in journeys:
+        dep = journey['timing']['departureTime']
+        price = None
+        for fare in journey['fares']:
+            if fare['classOfService']['code'] == 'STANDARD':
+                p = fare.get('prices')
+                if p and p.get('displayPrice'):
+                    price = int(p['displayPrice'])
+                break
+        prices[dep] = price
+    return prices