fix: 修复MaterialRepository中get_project_by_id方法的占位符实现

问题修复:
- 修复MaterialRepository.get_project_by_id总是返回None的问题
- 实现正确的项目查询逻辑，直接从projects表查询
- 解决AI分类后文件移动失败的根本原因

 技术实现:
- 在MaterialRepository中添加完整的项目查询实现
- 正确处理数据库查询和错误处理
- 支持项目不存在时返回None而不是错误

 问题解决:
- 现在AI分类完成后可以正确找到项目信息
- 文件移动到assets/分类目录功能将正常工作
- 消除了'项目不存在'的错误信息

apps/desktop/src-tauri/src/data/repositories/material_repository.rs

@@ -452,10 +452,44 @@ impl MaterialRepository {
     }
 
     /// 根据项目ID获取项目信息
-    pub async fn get_project_by_id(&self, _project_id: &str) -> Result<Option<crate::data::models::project::Project>> {
-        // 这里需要引用项目仓库，暂时返回None
-        // 在实际实现中，应该通过依赖注入获取项目仓库
-        Ok(None)
+    pub async fn get_project_by_id(&self, project_id: &str) -> Result<Option<crate::data::models::project::Project>> {
+        use crate::data::models::project::Project;
+        use chrono::{DateTime, Utc};
+
+        let conn = self.connection.lock().unwrap();
+
+        let mut stmt = conn.prepare(
+            "SELECT id, name, path, description, created_at, updated_at, is_active
+             FROM projects WHERE id = ?1"
+        )?;
+
+        let result = stmt.query_row([project_id], |row| {
+            let created_at_str: String = row.get(4)?;
+            let updated_at_str: String = row.get(5)?;
+
+            let created_at = DateTime::parse_from_rfc3339(&created_at_str)
+                .map_err(|_| rusqlite::Error::InvalidColumnType(4, "created_at".to_string(), rusqlite::types::Type::Text))?
+                .with_timezone(&Utc);
+            let updated_at = DateTime::parse_from_rfc3339(&updated_at_str)
+                .map_err(|_| rusqlite::Error::InvalidColumnType(5, "updated_at".to_string(), rusqlite::types::Type::Text))?
+                .with_timezone(&Utc);
+
+            Ok(Project {
+                id: row.get(0)?,
+                name: row.get(1)?,
+                path: row.get(2)?,
+                description: row.get(3)?,
+                created_at,
+                updated_at,
+                is_active: row.get::<_, i32>(6)? != 0,
+            })
+        });
+
+        match result {
+            Ok(project) => Ok(Some(project)),
+            Err(rusqlite::Error::QueryReturnedNoRows) => Ok(None),
+            Err(e) => Err(e.into()),
+        }
     }
 
     /// 根据片段ID获取片段信息