feat: add milestone and label management functionality (#39)

- Add comprehensive milestone CRUD operations (8 tools)
  - create_milestone, get_milestone, get_milestone_by_name
  - list_repo_milestones, edit_milestone, edit_milestone_by_name
  - delete_milestone, delete_milestone_by_name
- Add comprehensive label CRUD operations (9 tools)
  - create_label, get_repo_label, list_repo_labels
  - edit_label, delete_label, get_issue_labels
  - add_issue_labels, remove_issue_labels, replace_issue_labels
- Update README.md with new tool documentation
- Integrate with existing gitea-mcp architecture
- Support read-only mode and proper error handling

operation/operation.go

@@ -4,6 +4,8 @@ import (
 	"fmt"
 
 	"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/pull"
 	"gitea.com/gitea/gitea-mcp/operation/repo"
 	"gitea.com/gitea/gitea-mcp/operation/search"
@@ -30,6 +32,12 @@ func RegisterTool(s *server.MCPServer) {
 	// Pull Tool
 	s.AddTools(pull.Tool.Tools()...)
 
+	// Milestone Tool
+	s.AddTools(milestone.Tool.Tools()...)
+
+	// Label Tool
+	s.AddTools(label.Tool.Tools()...)
+
 	// Search Tool
 	s.AddTools(search.Tool.Tools()...)