refactor: extract StationSearchService

Audit item #8. StationController::index was ~100 lines doing the
haversine join, in-PHP filter/sort/group, search-row write, and
prediction call — well past the "thin orchestrator" line in
.claude/rules/architecture.md.

- App\Services\StationSearch\SearchCriteria — DTO (lat/lng/fuelType/
  radiusKm/sort)
- App\Services\StationSearch\SearchResult — DTO (stations, prices
  summary, reliability counts, prediction payload)
- App\Services\StationSearch\StationSearchService::search(criteria,
  ?user, ?ipHash) — owns the haversine query, the per-row reliability
  memoisation, sort, count, search-row logging, and the tier-gated
  prediction.

The controller now resolves coordinates, builds a SearchCriteria, calls
the service, and shapes the JSON response. Down from 154 → 71 lines.
Public API contract unchanged — all 15 StationController tests pass
without modification.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Services/StationSearch/SearchResult.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace App\Services\StationSearch;
+
+use Illuminate\Support\Collection;
+
+final readonly class SearchResult
+{
+    /**
+     * @param  Collection<int, mixed>  $stations  Sorted station rows with _updated_at/_reliability/_classification cached
+     * @param  array{lowest: ?int, highest: ?int, avg: ?float}  $pricesSummary
+     * @param  array{reliable: int, stale: int, outdated: int}  $reliabilityCounts
+     * @param  array<string, mixed>  $prediction
+     */
+    public function __construct(
+        public Collection $stations,
+        public array $pricesSummary,
+        public array $reliabilityCounts,
+        public array $prediction,
+    ) {}
+}