feat(admin): 新增通用KV系统配置管理接口

新增后台配置管理相关的表单请求类，添加通用设置的列表查询和更新接口，支持按分组筛选配置项并返回标准化的配置数据

app/Http/Controllers/Api/V1/Admin/AdminSettingController.php

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+<?php
+
+namespace App\Http\Controllers\Api\V1\Admin;
+
+use App\Http\Controllers\Controller;
+use App\Http\Requests\Admin\AdminSettingIndexRequest;
+use App\Http\Requests\Admin\AdminSettingUpdateRequest;
+use App\Models\LotterySetting;
+use App\Support\ApiResponse;
+use App\Services\LotterySettings;
+use Illuminate\Http\JsonResponse;
+
+/**
+ * 后台：运营配置（KV 设置）读写。
+ */
+final class AdminSettingController extends Controller
+{
+    public function index(AdminSettingIndexRequest $request): JsonResponse
+    {
+        $validated = $request->validated();
+        $query = LotterySetting::query()->orderBy('setting_key');
+
+        if (! empty($validated['group'])) {
+            $query->where('group_name', $validated['group']);
+        }
+
+        $items = $query->get()->map(fn (LotterySetting $s): array => [
+            'key' => $s->setting_key,
+            'value' => $s->value_json,
+            'group' => $s->group_name,
+            'description' => $s->description_zh,
+        ]);
+
+        return ApiResponse::success(['items' => $items]);
+    }
+
+    public function update(AdminSettingUpdateRequest $request, string $key): JsonResponse
+    {
+        $setting = LotterySetting::query()->where('setting_key', $key)->first();
+        if ($setting === null) {
+            return ApiResponse::error('Setting not found', 404);
+        }
+
+        LotterySettings::put(
+            $key,
+            $request->validated('value'),
+            $setting->group_name,
+            $setting->description_zh,
+        );
+
+        $fresh = LotterySetting::query()->where('setting_key', $key)->first();
+
+        return ApiResponse::success([
+            'key' => $fresh->setting_key,
+            'value' => $fresh->value_json,
+            'group' => $fresh->group_name,
+            'description' => $fresh->description_zh,
+        ]);
+    }
+}

app/Http/Requests/Admin/AdminSettingIndexRequest.php

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+<?php
+
+namespace App\Http\Requests\Admin;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+final class AdminSettingIndexRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'group' => ['sometimes', 'nullable', 'string', 'max:64'],
+        ];
+    }
+}

app/Http/Requests/Admin/AdminSettingUpdateRequest.php

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+<?php
+
+namespace App\Http\Requests\Admin;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+final class AdminSettingUpdateRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'value' => ['required'],
+        ];
+    }
+}