feat: add PostcodeService and price validation with DB constraints

- Add PostcodeService to resolve UK postcodes, outcodes, and place names to coordinates via postcodes.io API with 30-day caching
- Add LocationResult value object for resolved location data
- Add per-fuel-type price validation (80p-1050p range) to FuelPriceService with warning logs for out-of-range prices
- Change price_pence column from unsignedSmallInteger to unsignedMediumInteger in station_prices tables
- Add CHECK constraints (5000-50000 range) on price_pence columns as database-level guard
- Improve error handling in PollFuelPrices command with file/line/trace output
- Add tests for PostcodeService covering full postcodes, outcodes, place names, caching, and error handling
- Add test for price validation range checks

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

app/Console/Commands/PollFuelPrices.php

@@ -31,6 +31,8 @@ class PollFuelPrices extends Command
             PricesUpdatedEvent::dispatch($inserted, $fullRefresh);
         } catch (Throwable $e) {
             $this->error("Poll failed: {$e->getMessage()}");
+            $this->error("In {$e->getFile()}:{$e->getLine()}");
+            $this->line($e->getTraceAsString());
 
             return self::FAILURE;
         }