feat: initialize Nuanji (Warm Notes) project

- Base platform from base.git (ERP base: auth, core, config, message, workflow, plugin)
- Created erp-diary module skeleton (lib.rs, dto.rs, error.rs, event.rs, state.rs)
- Integrated erp-diary into workspace and erp-server
- Added DiaryModule registration in main.rs
- Added DiaryState FromRef in state.rs
- Diary routes mounted (empty routes, ready for implementation)
- Product design spec v1.2 preserved in docs/
- Implementation plan preserved in plans/

Cargo check: OK
Cargo test: OK (78+ base tests passing)

crates/erp-message/src/error.rs

@@ -0,0 +1,144 @@
+use erp_core::error::AppError;
+
+/// 消息中心模块错误类型。
+#[derive(Debug, thiserror::Error)]
+pub enum MessageError {
+    #[error("验证失败: {0}")]
+    Validation(String),
+
+    #[error("未找到: {0}")]
+    NotFound(String),
+
+    #[error("模板编码已存在: {0}")]
+    DuplicateTemplateCode(String),
+
+    #[error("渲染失败: {0}")]
+    TemplateRenderError(String),
+
+    #[error("版本冲突: 数据已被其他操作修改，请刷新后重试")]
+    VersionMismatch,
+}
+
+impl From<MessageError> for AppError {
+    fn from(err: MessageError) -> Self {
+        match err {
+            MessageError::Validation(msg) => AppError::Validation(msg),
+            MessageError::NotFound(msg) => AppError::NotFound(msg),
+            MessageError::DuplicateTemplateCode(msg) => AppError::Conflict(msg),
+            MessageError::TemplateRenderError(msg) => AppError::Internal(msg),
+            MessageError::VersionMismatch => AppError::VersionMismatch,
+        }
+    }
+}
+
+impl From<sea_orm::TransactionError<MessageError>> for MessageError {
+    fn from(err: sea_orm::TransactionError<MessageError>) -> Self {
+        match err {
+            sea_orm::TransactionError::Connection(db_err) => {
+                MessageError::Validation(db_err.to_string())
+            }
+            sea_orm::TransactionError::Transaction(msg_err) => msg_err,
+        }
+    }
+}
+
+pub type MessageResult<T> = Result<T, MessageError>;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use erp_core::error::AppError;
+
+    #[test]
+    fn validation_maps_to_app_validation() {
+        let app: AppError = MessageError::Validation("标题不能为空".to_string()).into();
+        match app {
+            AppError::Validation(msg) => assert_eq!(msg, "标题不能为空"),
+            other => panic!("Expected AppError::Validation, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn not_found_maps_to_app_not_found() {
+        let app: AppError = MessageError::NotFound("消息不存在".to_string()).into();
+        match app {
+            AppError::NotFound(msg) => assert_eq!(msg, "消息不存在"),
+            other => panic!("Expected AppError::NotFound, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn duplicate_template_code_maps_to_app_conflict() {
+        let app: AppError = MessageError::DuplicateTemplateCode("WELCOME".to_string()).into();
+        match app {
+            AppError::Conflict(msg) => assert_eq!(msg, "WELCOME"),
+            other => panic!("Expected AppError::Conflict, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn template_render_error_maps_to_app_internal() {
+        let app: AppError = MessageError::TemplateRenderError("变量缺失".to_string()).into();
+        match app {
+            AppError::Internal(msg) => assert_eq!(msg, "变量缺失"),
+            other => panic!("Expected AppError::Internal, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn version_mismatch_maps_to_app_version_mismatch() {
+        let app: AppError = MessageError::VersionMismatch.into();
+        match app {
+            AppError::VersionMismatch => {}
+            other => panic!("Expected AppError::VersionMismatch, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn error_display_format() {
+        assert_eq!(
+            MessageError::Validation("字段为空".to_string()).to_string(),
+            "验证失败: 字段为空"
+        );
+        assert_eq!(
+            MessageError::NotFound("id=123".to_string()).to_string(),
+            "未找到: id=123"
+        );
+        assert_eq!(
+            MessageError::DuplicateTemplateCode("CODE".to_string()).to_string(),
+            "模板编码已存在: CODE"
+        );
+        assert_eq!(
+            MessageError::TemplateRenderError("解析失败".to_string()).to_string(),
+            "渲染失败: 解析失败"
+        );
+        assert_eq!(
+            MessageError::VersionMismatch.to_string(),
+            "版本冲突: 数据已被其他操作修改，请刷新后重试"
+        );
+    }
+
+    #[test]
+    fn transaction_connection_error_maps_to_validation() {
+        let db_err = sea_orm::DbErr::Conn(sea_orm::RuntimeErr::Internal("连接超时".to_string()));
+        let tx_err: sea_orm::TransactionError<MessageError> =
+            sea_orm::TransactionError::Connection(db_err);
+        let msg_err: MessageError = tx_err.into();
+        match msg_err {
+            MessageError::Validation(msg) => assert!(msg.contains("连接超时")),
+            other => panic!("期望 Validation，得到 {:?}", other),
+        }
+    }
+
+    #[test]
+    fn transaction_inner_error_passthrough() {
+        let inner = MessageError::NotFound("模板不存在".to_string());
+        let tx_err: sea_orm::TransactionError<MessageError> =
+            sea_orm::TransactionError::Transaction(inner);
+        let msg_err: MessageError = tx_err.into();
+        match msg_err {
+            MessageError::NotFound(msg) => assert_eq!(msg, "模板不存在"),
+            other => panic!("期望 NotFound，得到 {:?}", other),
+        }
+    }
+}