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>

tests/Unit/Services/FuelPriceServiceTest.php

@@ -252,6 +252,51 @@ it('skips unknown fuel types without error', function (): void {
         ->and(StationPrice::count())->toBe(0);
 });
 
+it('skips prices outside valid range and logs a warning', function (): void {
+    Cache::put('fuel_finder_access_token', 'tok', 3540);
+
+    Station::factory()->create(['node_id' => 'sta1']);
+
+    Http::fake([
+        '*/pfs/fuel-prices*' => Http::sequence()
+            ->push([
+                [
+                    'node_id' => 'sta1',
+                    'fuel_prices' => [
+                        // Way too high — clearly bad data
+                        [
+                            'fuel_type' => 'E10',
+                            'price' => 900.0,
+                            'price_last_updated' => '2026-04-04T10:00:00.000Z',
+                            'price_change_effective_timestamp' => '2026-04-04T10:00:00.000Z',
+                        ],
+                        // Too low — below minimum
+                        [
+                            'fuel_type' => 'E5',
+                            'price' => 10.0,
+                            'price_last_updated' => '2026-04-04T10:00:00.000Z',
+                            'price_change_effective_timestamp' => '2026-04-04T10:00:00.000Z',
+                        ],
+                        // Valid — should be inserted
+                        [
+                            'fuel_type' => 'B7_STANDARD',
+                            'price' => 155.9,
+                            'price_last_updated' => '2026-04-04T10:00:00.000Z',
+                            'price_change_effective_timestamp' => '2026-04-04T10:00:00.000Z',
+                        ],
+                    ],
+                ],
+            ])
+            ->push([]),
+    ]);
+
+    $inserted = $this->service->pollPrices();
+
+    expect($inserted)->toBe(1)
+        ->and(StationPrice::count())->toBe(1)
+        ->and(StationPrice::first()->price_pence)->toBe(15590);
+});
+
 it('stops pagination when an empty batch is returned', function (): void {
     Cache::put('fuel_finder_access_token', 'tok', 3540);