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/runner/tasks/exec_seams.go

@@ -0,0 +1,7 @@
+package tasks
+
+import "os/exec"
+
+// execCommand is a seam for process execution in tests.
+var execCommand = exec.Command
+