feat: persist postcodes.io fallback results into local DB

tests/Unit/Services/PostcodeServiceTest.php

@@ -216,3 +216,48 @@ it('resolves an outcode from local DB without calling HTTP', function (): void {
 
     Http::assertNothingSent();
 });
+
+// --- HTTP fallback persistence ---
+
+it('persists a full postcode resolved via HTTP fallback', function (): void {
+    Http::fake([
+        '*/postcodes/SW1A1AA' => Http::response([
+            'status' => 200,
+            'result' => [
+                'postcode' => 'SW1A 1AA',
+                'latitude' => 51.501009,
+                'longitude' => -0.141588,
+            ],
+        ]),
+    ]);
+
+    $this->service->resolve('SW1A 1AA');
+
+    $row = Postcode::find('SW1A1AA');
+
+    expect($row)->not->toBeNull()
+        ->and($row->outcode)->toBe('SW1A')
+        ->and((float) $row->lat)->toBe(51.501009)
+        ->and((float) $row->lng)->toBe(-0.141588);
+});
+
+it('persists an outcode resolved via HTTP fallback', function (): void {
+    Http::fake([
+        '*/outcodes/PE7' => Http::response([
+            'status' => 200,
+            'result' => [
+                'outcode' => 'PE7',
+                'latitude' => 52.536397,
+                'longitude' => -0.210181,
+            ],
+        ]),
+    ]);
+
+    $this->service->resolve('PE7');
+
+    $row = Outcode::find('PE7');
+
+    expect($row)->not->toBeNull()
+        ->and((float) $row->lat)->toBe(52.536397)
+        ->and((float) $row->lng)->toBe(-0.210181);
+});