feat: add cleanup for unbound addresses feature (#739)

- Add unboundAddress cleanup type to backend cleanup logic
- Update CleanupSettings model with unbound address fields
- Add scheduled task for automatic unbound address cleanup
- Add UI controls in admin Maintenance panel for manual cleanup
- Add i18n support (en/zh) for unbound address cleanup labels
- Clean addresses not bound to any user created before n days

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

frontend/src/views/admin/Maintenance.vue

@@ -17,6 +17,8 @@ const cleanupModel = ref({
     cleanAddressDays: 30,
     enableInactiveAddressAutoCleanup: false,
     cleanInactiveAddressDays: 30,
+    enableUnboundAddressAutoCleanup: false,
+    cleanUnboundAddressDays: 30,
 })
 
 const { t } = useI18n({
@@ -28,6 +30,7 @@ const { t } = useI18n({
             sendBoxLabel: "Cleanup the sendbox before n days",
             addressCreateLabel: "Cleanup the address created before n days",
             inactiveAddressLabel: "Cleanup the inactive address before n days",
+            unboundAddressLabel: "Cleanup the unbound address before n days",
             cleanupNow: "Cleanup now",
             autoCleanup: "Auto cleanup",
             cleanupSuccess: "Cleanup success",
@@ -41,6 +44,7 @@ const { t } = useI18n({
             sendBoxLabel: "清理 n 天前的发件箱",
             addressCreateLabel: "清理 n 天前创建的地址",
             inactiveAddressLabel: "清理 n 天前的未活跃地址",
+            unboundAddressLabel: "清理 n 天前的未绑定用户地址",
             autoCleanup: "自动清理",
             cleanupSuccess: "清理成功",
             cleanupNow: "立即清理",
@@ -161,6 +165,18 @@ onMounted(async () => {
                         {{ t('cleanupNow') }}
                     </n-button>
                 </n-form-item-row>
+                <n-form-item-row :label="t('unboundAddressLabel')">
+                    <n-checkbox v-model:checked="cleanupModel.enableUnboundAddressAutoCleanup">
+                        {{ t('autoCleanup') }}
+                    </n-checkbox>
+                    <n-input-number v-model:value="cleanupModel.cleanUnboundAddressDays" :placeholder="t('tip')" />
+                    <n-button @click="cleanup('unboundAddress', cleanupModel.cleanUnboundAddressDays)">
+                        <template #icon>
+                            <n-icon :component="CleaningServicesFilled" />
+                        </template>
+                        {{ t('cleanupNow') }}
+                    </n-button>
+                </n-form-item-row>
             </n-form>
         </n-card>
     </div>