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/template_service.rs

@@ -0,0 +1,116 @@
+use chrono::Utc;
+use sea_orm::{
+    ActiveModelTrait, ColumnTrait, EntityTrait, PaginatorTrait, QueryFilter, Set,
+};
+use uuid::Uuid;
+
+use crate::dto::{CreateTemplateReq, MessageTemplateResp};
+use crate::entity::message_template;
+use crate::error::{MessageError, MessageResult};
+
+/// 消息模板服务。
+pub struct TemplateService;
+
+impl TemplateService {
+    /// 查询模板列表。
+    pub async fn list(
+        tenant_id: Uuid,
+        page: u64,
+        page_size: u64,
+        db: &sea_orm::DatabaseConnection,
+    ) -> MessageResult<(Vec<MessageTemplateResp>, u64)> {
+        let paginator = message_template::Entity::find()
+            .filter(message_template::Column::TenantId.eq(tenant_id))
+            .filter(message_template::Column::DeletedAt.is_null())
+            .paginate(db, page_size);
+
+        let total = paginator
+            .num_items()
+            .await
+            .map_err(|e| MessageError::Validation(e.to_string()))?;
+
+        let page_index = page.saturating_sub(1);
+        let models = paginator
+            .fetch_page(page_index)
+            .await
+            .map_err(|e| MessageError::Validation(e.to_string()))?;
+
+        let resps = models.iter().map(Self::model_to_resp).collect();
+        Ok((resps, total))
+    }
+
+    /// 创建消息模板。
+    pub async fn create(
+        tenant_id: Uuid,
+        operator_id: Uuid,
+        req: &CreateTemplateReq,
+        db: &sea_orm::DatabaseConnection,
+    ) -> MessageResult<MessageTemplateResp> {
+        // 检查编码唯一性
+        let existing = message_template::Entity::find()
+            .filter(message_template::Column::TenantId.eq(tenant_id))
+            .filter(message_template::Column::Code.eq(&req.code))
+            .filter(message_template::Column::DeletedAt.is_null())
+            .one(db)
+            .await
+            .map_err(|e| MessageError::Validation(e.to_string()))?;
+
+        if existing.is_some() {
+            return Err(MessageError::DuplicateTemplateCode(format!(
+                "模板编码已存在: {}",
+                req.code
+            )));
+        }
+
+        let id = Uuid::now_v7();
+        let now = Utc::now();
+
+        let model = message_template::ActiveModel {
+            id: Set(id),
+            tenant_id: Set(tenant_id),
+            name: Set(req.name.clone()),
+            code: Set(req.code.clone()),
+            channel: Set(req.channel.clone()),
+            title_template: Set(req.title_template.clone()),
+            body_template: Set(req.body_template.clone()),
+            language: Set(req.language.clone()),
+            created_at: Set(now),
+            updated_at: Set(now),
+            created_by: Set(operator_id),
+            updated_by: Set(operator_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))
+    }
+
+    /// 使用模板渲染消息内容。
+    /// 支持 {{variable}} 格式的变量插值。
+    pub fn render(template: &str, variables: &std::collections::HashMap<String, String>) -> String {
+        let mut result = template.to_string();
+        for (key, value) in variables {
+            result = result.replace(&format!("{{{{{}}}}}", key), value);
+        }
+        result
+    }
+
+    fn model_to_resp(m: &message_template::Model) -> MessageTemplateResp {
+        MessageTemplateResp {
+            id: m.id,
+            tenant_id: m.tenant_id,
+            name: m.name.clone(),
+            code: m.code.clone(),
+            channel: m.channel.clone(),
+            title_template: m.title_template.clone(),
+            body_template: m.body_template.clone(),
+            language: m.language.clone(),
+            created_at: m.created_at,
+            updated_at: m.updated_at,
+        }
+    }
+}