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>

database/migrations/2026_04_04_093343_change_price_pence_to_mediumint_in_station_prices.php

@@ -0,0 +1,44 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('station_prices', function (Blueprint $table): void {
+            $table->unsignedMediumInteger('price_pence')
+                ->comment('Price in pence × 100, e.g. 15990 = 159.90p')
+                ->change();
+        });
+
+        Schema::table('station_prices_current', function (Blueprint $table): void {
+            $table->unsignedMediumInteger('price_pence')
+                ->comment('Price in pence × 100, e.g. 15990 = 159.90p')
+                ->change();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('station_prices', function (Blueprint $table): void {
+            $table->unsignedSmallInteger('price_pence')
+                ->comment('Price in pence × 100')
+                ->change();
+        });
+
+        Schema::table('station_prices_current', function (Blueprint $table): void {
+            $table->unsignedSmallInteger('price_pence')
+                ->comment('Price in pence × 100, e.g. 15990 = 159.90p')
+                ->change();
+        });
+    }
+};

database/migrations/2026_04_04_093705_add_price_pence_check_constraint_to_station_prices.php

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+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+
+/**
+ * Add database-level CHECK constraint on price_pence (MySQL only).
+ *
+ * Range: 5 000–50 000 = 50p–500p per litre.
+ * This is a broad last-resort guard; the application layer enforces
+ * tighter per-fuel-type limits before any insert reaches the DB.
+ */
+return new class extends Migration
+{
+    public function up(): void
+    {
+        if (DB::getDriverName() !== 'mysql') {
+            return;
+        }
+
+        DB::statement('ALTER TABLE station_prices ADD CONSTRAINT chk_price_pence_range CHECK (price_pence BETWEEN 5000 AND 50000)');
+        DB::statement('ALTER TABLE station_prices_current ADD CONSTRAINT chk_current_price_pence_range CHECK (price_pence BETWEEN 5000 AND 50000)');
+    }
+
+    public function down(): void
+    {
+        if (DB::getDriverName() !== 'mysql') {
+            return;
+        }
+
+        DB::statement('ALTER TABLE station_prices DROP CHECK chk_price_pence_range');
+        DB::statement('ALTER TABLE station_prices_current DROP CHECK chk_current_price_pence_range');
+    }
+};