Add notification_read and notification_write tools (#172)

Add notification management via two new MCP tools using the method-dispatch pattern:

- `notification_read`: list notifications (global or repo-scoped, with status/subject_type/since/before filters) and get single notification thread by ID
- `notification_write`: mark single notification as read, mark all notifications as read (global or repo-scoped)

---
This PR was written with the help of Claude Opus 4.6

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/172
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

operation/operation.go

@@ -15,6 +15,7 @@ import (
 	"gitea.com/gitea/gitea-mcp/operation/issue"
 	"gitea.com/gitea/gitea-mcp/operation/label"
 	"gitea.com/gitea/gitea-mcp/operation/milestone"
+	"gitea.com/gitea/gitea-mcp/operation/notification"
 	"gitea.com/gitea/gitea-mcp/operation/pull"
 	"gitea.com/gitea/gitea-mcp/operation/repo"
 	"gitea.com/gitea/gitea-mcp/operation/search"
@@ -41,6 +42,9 @@ func RegisterTool(s *server.MCPServer) {
 	// Repo Tool
 	s.AddTools(repo.Tool.Tools()...)
 
+	// Notification Tool
+	s.AddTools(notification.Tool.Tools()...)
+
 	// Issue Tool
 	s.AddTools(issue.Tool.Tools()...)