feat(cleanup): 解耦 request_candidates 与 provider_api_keys 生命周期

- 移除 request_candidates.key_id 对 provider_api_keys 的外键约束(含迁移脚本)
- 删除 Key 时不再级联删除候选记录，改为独立按保留天数定时清理
- 新增 request_candidates_retention_days / request_candidates_cleanup_batch_size 配置项
- batch_delete_task 增加 lock_timeout 及超时自动降批重试机制
- cleanup_key_references 提取阶段化清理流程，移除 RequestCandidate 联动删除
- 前端 CleanupPolicySection 新增候选记录保留天数和清理批次配置

Closes #227

Co-authored-by: Entropy-Xu <entropy.xu@cloudhabitatsh.com>

frontend/src/views/admin/SystemSettings.vue

@@ -99,6 +99,8 @@
             :log-retention-days="systemConfig.log_retention_days"
             :cleanup-batch-size="systemConfig.cleanup_batch_size"
             :audit-log-retention-days="systemConfig.audit_log_retention_days"
+            :request-candidates-retention-days="systemConfig.request_candidates_retention_days"
+            :request-candidates-cleanup-batch-size="systemConfig.request_candidates_cleanup_batch_size"
             :loading="cleanupConfigLoading"
             :has-changes="hasCleanupConfigChanges"
             @save="saveCleanupConfig"
@@ -109,6 +111,8 @@
             @update:log-retention-days="systemConfig.log_retention_days = $event"
             @update:cleanup-batch-size="systemConfig.cleanup_batch_size = $event"
             @update:audit-log-retention-days="systemConfig.audit_log_retention_days = $event"
+            @update:request-candidates-retention-days="systemConfig.request_candidates_retention_days = $event"
+            @update:request-candidates-cleanup-batch-size="systemConfig.request_candidates_cleanup_batch_size = $event"
           />
 
           <!-- 定时任务 -->

frontend/src/views/admin/system-settings/CleanupPolicySection.vue

@@ -152,6 +152,46 @@
           超过后删除审计日志记录
         </p>
       </div>
+
+      <div>
+        <Label
+          for="request-candidates-retention-days"
+          class="block text-sm font-medium"
+        >
+          候选记录保留天数
+        </Label>
+        <Input
+          id="request-candidates-retention-days"
+          :model-value="requestCandidatesRetentionDays"
+          type="number"
+          placeholder="30"
+          class="mt-1"
+          @update:model-value="$emit('update:requestCandidatesRetentionDays', Number($event))"
+        />
+        <p class="mt-1 text-xs text-muted-foreground">
+          过期后按时间窗口批量清理 request_candidates 审计记录
+        </p>
+      </div>
+
+      <div>
+        <Label
+          for="request-candidates-cleanup-batch-size"
+          class="block text-sm font-medium"
+        >
+          候选记录清理批次
+        </Label>
+        <Input
+          id="request-candidates-cleanup-batch-size"
+          :model-value="requestCandidatesCleanupBatchSize"
+          type="number"
+          placeholder="5000"
+          class="mt-1"
+          @update:model-value="$emit('update:requestCandidatesCleanupBatchSize', Number($event))"
+        />
+        <p class="mt-1 text-xs text-muted-foreground">
+          独立控制候选记录大表清理节奏，不再跟随 Key 删除联动
+        </p>
+      </div>
     </div>
 
     <!-- 清理策略说明 -->
@@ -164,7 +204,7 @@
         <p>2. <strong>压缩日志阶段</strong>: body 字段被压缩存储，节省空间</p>
         <p>3. <strong>统计阶段</strong>: 仅保留 tokens、成本等统计信息</p>
         <p>4. <strong>归档删除</strong>: 超过保留期限后完全删除记录</p>
-        <p>5. <strong>候选记录</strong>: 与详细记录同步清理请求候选记录（request_candidates）</p>
+        <p>5. <strong>候选记录</strong>: 独立按保留天数清理 request_candidates 审计记录，不再跟随 Key 删除联动</p>
         <p>6. <strong>审计日志</strong>: 独立清理，记录用户登录、操作等安全事件</p>
       </div>
     </div>
@@ -186,6 +226,8 @@ defineProps<{
   logRetentionDays: number
   cleanupBatchSize: number
   auditLogRetentionDays: number
+  requestCandidatesRetentionDays: number
+  requestCandidatesCleanupBatchSize: number
   loading: boolean
   hasChanges: boolean
 }>()
@@ -199,5 +241,7 @@ defineEmits<{
   'update:logRetentionDays': [value: number]
   'update:cleanupBatchSize': [value: number]
   'update:auditLogRetentionDays': [value: number]
+  'update:requestCandidatesRetentionDays': [value: number]
+  'update:requestCandidatesCleanupBatchSize': [value: number]
 }>()
 </script>

frontend/src/views/admin/system-settings/composables/useSystemConfig.ts

@@ -32,6 +32,8 @@ export interface SystemConfig {
   log_retention_days: number
   cleanup_batch_size: number
   audit_log_retention_days: number
+  request_candidates_retention_days: number
+  request_candidates_cleanup_batch_size: number
   // 定时任务
   enable_provider_checkin: boolean
   provider_checkin_time: string
@@ -66,6 +68,8 @@ const CONFIG_KEYS = [
   'log_retention_days',
   'cleanup_batch_size',
   'audit_log_retention_days',
+  'request_candidates_retention_days',
+  'request_candidates_cleanup_batch_size',
   // 定时任务
   'enable_provider_checkin',
   'provider_checkin_time',
@@ -101,6 +105,8 @@ function createDefaultConfig(): SystemConfig {
     log_retention_days: 365,
     cleanup_batch_size: 1000,
     audit_log_retention_days: 30,
+    request_candidates_retention_days: 30,
+    request_candidates_cleanup_batch_size: 5000,
     // 定时任务
     enable_provider_checkin: true,
     provider_checkin_time: '01:05',
@@ -171,7 +177,11 @@ export function useSystemConfig() {
       systemConfig.value.log_retention_days !== originalConfig.value.log_retention_days ||
       systemConfig.value.cleanup_batch_size !== originalConfig.value.cleanup_batch_size ||
       systemConfig.value.audit_log_retention_days !==
-      originalConfig.value.audit_log_retention_days
+      originalConfig.value.audit_log_retention_days ||
+      systemConfig.value.request_candidates_retention_days !==
+      originalConfig.value.request_candidates_retention_days ||
+      systemConfig.value.request_candidates_cleanup_batch_size !==
+      originalConfig.value.request_candidates_cleanup_batch_size
     )
   })
 
@@ -421,6 +431,16 @@ export function useSystemConfig() {
           value: systemConfig.value.audit_log_retention_days,
           description: '审计日志保留天数',
         },
+        {
+          key: 'request_candidates_retention_days',
+          value: systemConfig.value.request_candidates_retention_days,
+          description: '请求候选记录保留天数',
+        },
+        {
+          key: 'request_candidates_cleanup_batch_size',
+          value: systemConfig.value.request_candidates_cleanup_batch_size,
+          description: '请求候选记录每批次清理条数',
+        },
       ]
 
       await Promise.all(
@@ -438,6 +458,10 @@ export function useSystemConfig() {
         originalConfig.value.cleanup_batch_size = systemConfig.value.cleanup_batch_size
         originalConfig.value.audit_log_retention_days =
           systemConfig.value.audit_log_retention_days
+        originalConfig.value.request_candidates_retention_days =
+          systemConfig.value.request_candidates_retention_days
+        originalConfig.value.request_candidates_cleanup_batch_size =
+          systemConfig.value.request_candidates_cleanup_batch_size
       }
       success('请求记录清理配置已保存')
     } catch (err) {