Add tests for main package, manager, and various components

- Introduced unit tests for the main package to ensure compilation.
- Added tests for the manager, including validation of upload sessions and handling of Blender binary paths.
- Implemented tests for job token generation and validation, ensuring security and integrity.
- Created tests for configuration management and database schema to verify functionality.
- Added tests for logger and runner components to enhance overall test coverage and reliability.

internal/manager/manager.go

@@ -630,6 +630,13 @@ func (s *Manager) respondError(w http.ResponseWriter, status int, message string
 	s.respondJSON(w, status, map[string]string{"error": message})
 }
 
+func (s *Manager) respondErrorWithCode(w http.ResponseWriter, status int, code, message string) {
+	s.respondJSON(w, status, map[string]string{
+		"error": message,
+		"code":  code,
+	})
+}
+
 // createSessionCookie creates a secure session cookie with appropriate flags for the environment
 func (s *Manager) createSessionCookie(sessionID string) *http.Cookie {
 	cookie := &http.Cookie{