feat(message): add message center module (Phase 5)

Implement the complete message center with:
- Database migrations for message_templates, messages, message_subscriptions tables
- erp-message crate with entities, DTOs, services, handlers
- Message CRUD, send, read/unread tracking, soft delete
- Template management with variable interpolation
- Subscription preferences with DND support
- Frontend: messages page, notification panel, unread count badge
- Server integration with module registration and routing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

crates/erp-message/src/service/subscription_service.rs

@@ -0,0 +1,116 @@
+use chrono::Utc;
+use sea_orm::{ActiveModelTrait, ColumnTrait, EntityTrait, QueryFilter, Set};
+use uuid::Uuid;
+
+use crate::dto::{MessageSubscriptionResp, UpdateSubscriptionReq};
+use crate::entity::message_subscription;
+use crate::error::{MessageError, MessageResult};
+
+/// 消息订阅偏好服务。
+pub struct SubscriptionService;
+
+impl SubscriptionService {
+    /// 获取用户订阅偏好。
+    pub async fn get(
+        tenant_id: Uuid,
+        user_id: Uuid,
+        db: &sea_orm::DatabaseConnection,
+    ) -> MessageResult<MessageSubscriptionResp> {
+        let model = message_subscription::Entity::find()
+            .filter(message_subscription::Column::TenantId.eq(tenant_id))
+            .filter(message_subscription::Column::UserId.eq(user_id))
+            .filter(message_subscription::Column::DeletedAt.is_null())
+            .one(db)
+            .await
+            .map_err(|e| MessageError::Validation(e.to_string()))?
+            .ok_or_else(|| MessageError::NotFound("订阅偏好不存在".to_string()))?;
+
+        Ok(Self::model_to_resp(&model))
+    }
+
+    /// 创建或更新用户订阅偏好（upsert）。
+    pub async fn upsert(
+        tenant_id: Uuid,
+        user_id: Uuid,
+        req: &UpdateSubscriptionReq,
+        db: &sea_orm::DatabaseConnection,
+    ) -> MessageResult<MessageSubscriptionResp> {
+        let existing = message_subscription::Entity::find()
+            .filter(message_subscription::Column::TenantId.eq(tenant_id))
+            .filter(message_subscription::Column::UserId.eq(user_id))
+            .filter(message_subscription::Column::DeletedAt.is_null())
+            .one(db)
+            .await
+            .map_err(|e| MessageError::Validation(e.to_string()))?;
+
+        let now = Utc::now();
+
+        if let Some(model) = existing {
+            let mut active: message_subscription::ActiveModel = model.into();
+            if let Some(types) = &req.notification_types {
+                active.notification_types = Set(Some(types.clone()));
+            }
+            if let Some(prefs) = &req.channel_preferences {
+                active.channel_preferences = Set(Some(prefs.clone()));
+            }
+            if let Some(dnd) = req.dnd_enabled {
+                active.dnd_enabled = Set(dnd);
+            }
+            if let Some(ref start) = req.dnd_start {
+                active.dnd_start = Set(Some(start.clone()));
+            }
+            if let Some(ref end) = req.dnd_end {
+                active.dnd_end = Set(Some(end.clone()));
+            }
+            active.updated_at = Set(now);
+            active.updated_by = Set(user_id);
+
+            let updated = active
+                .update(db)
+                .await
+                .map_err(|e| MessageError::Validation(e.to_string()))?;
+
+            Ok(Self::model_to_resp(&updated))
+        } else {
+            let id = Uuid::now_v7();
+
+            let model = message_subscription::ActiveModel {
+                id: Set(id),
+                tenant_id: Set(tenant_id),
+                user_id: Set(user_id),
+                notification_types: Set(req.notification_types.clone()),
+                channel_preferences: Set(req.channel_preferences.clone()),
+                dnd_enabled: Set(req.dnd_enabled.unwrap_or(false)),
+                dnd_start: Set(req.dnd_start.clone()),
+                dnd_end: Set(req.dnd_end.clone()),
+                created_at: Set(now),
+                updated_at: Set(now),
+                created_by: Set(user_id),
+                updated_by: Set(user_id),
+                deleted_at: Set(None),
+            };
+
+            let inserted = model
+                .insert(db)
+                .await
+                .map_err(|e| MessageError::Validation(e.to_string()))?;
+
+            Ok(Self::model_to_resp(&inserted))
+        }
+    }
+
+    fn model_to_resp(m: &message_subscription::Model) -> MessageSubscriptionResp {
+        MessageSubscriptionResp {
+            id: m.id,
+            tenant_id: m.tenant_id,
+            user_id: m.user_id,
+            notification_types: m.notification_types.clone(),
+            channel_preferences: m.channel_preferences.clone(),
+            dnd_enabled: m.dnd_enabled,
+            dnd_start: m.dnd_start.clone(),
+            dnd_end: m.dnd_end.clone(),
+            created_at: m.created_at,
+            updated_at: m.updated_at,
+        }
+    }
+}