Reverse-geocode a general area label for logged searches

Each search now stores an `area_label` (district/town) reverse-geocoded from its
coarsened ~1km lat/lng bucket via postcodes.io, surfaced in the Filament Searches
admin as a sortable/searchable column plus an area filter. Geocoding is cached 30
days per bucket, queries a 2km radius so low-density buckets still match the
default 100m miss, and fails gracefully to null. Adds `searches:backfill-areas`
(scheduled hourly) to label existing rows and retry stragglers.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/Unit/Services/PostcodeServiceTest.php

@@ -279,3 +279,76 @@ it('persists an outcode resolved via HTTP fallback', function (): void {
         ->and((float) $row->lat)->toBe(52.536397)
         ->and((float) $row->lng)->toBe(-0.210181);
 });
+
+// --- Reverse geocoding (area label) ---
+
+it('reverse-geocodes coordinates to the admin district', function (): void {
+    Http::fake([
+        '*/postcodes?*' => Http::response([
+            'status' => 200,
+            'result' => [
+                ['admin_district' => 'Peterborough', 'region' => 'East of England'],
+            ],
+        ]),
+    ]);
+
+    expect($this->service->reverseResolve(52.5364, -0.2102))->toBe('Peterborough');
+});
+
+it('falls back to a broader area when admin district is missing', function (): void {
+    Http::fake([
+        '*/postcodes?*' => Http::response([
+            'status' => 200,
+            'result' => [
+                ['admin_district' => null, 'region' => 'Scotland'],
+            ],
+        ]),
+    ]);
+
+    expect($this->service->reverseResolve(57.4, -4.2))->toBe('Scotland');
+});
+
+it('returns null when reverse geocoding finds no area', function (): void {
+    Http::fake([
+        '*/postcodes?*' => Http::response(['status' => 200, 'result' => null]),
+    ]);
+
+    expect($this->service->reverseResolve(0.0, 0.0))->toBeNull();
+});
+
+it('returns null when the reverse geocode request fails', function (): void {
+    Http::fake([
+        '*/postcodes?*' => Http::response([], 500),
+    ]);
+
+    expect($this->service->reverseResolve(52.5364, -0.2102))->toBeNull();
+});
+
+it('caches the reverse-geocoded area per bucket', function (): void {
+    Http::fake([
+        '*/postcodes?*' => Http::response([
+            'status' => 200,
+            'result' => [['admin_district' => 'Peterborough']],
+        ]),
+    ]);
+
+    // Two coordinates inside the same ~1km (2dp) bucket → one HTTP call.
+    $this->service->reverseResolve(52.5364, -0.2102);
+    $this->service->reverseResolve(52.5359, -0.2148);
+
+    Http::assertSentCount(1);
+});
+
+it('queries postcodes.io with a wide radius so low-density buckets still match', function (): void {
+    Http::fake([
+        '*/postcodes?*' => Http::response([
+            'status' => 200,
+            'result' => [['admin_district' => 'Peterborough']],
+        ]),
+    ]);
+
+    $this->service->reverseResolve(52.54, -0.25);
+
+    // The default 100m radius misses the bucket centroid in rural areas; we send 2000m.
+    Http::assertSent(fn ($request) => str_contains($request->url(), 'radius=2000'));
+});