refactor: remove model abstraction and obsolete commands

refactor: remove model abstraction and obsolete commands

Remove the Model class and all model-related configuration, switching

the task processor to use a single server-side model. This eliminates

the local model selection hierarchy (TOCOMPUTE > skill > default).

Deleted commands:

- ListModelsCommand — no longer needed without local model registry

- JoinFilesCommand — superseded by other workflows

Updated AddTaskHeaderCommand to stop prompting for model alias and

generating model= in TOCOMPUTE headers.

Updated Task, TaskProcess, and TaskProcessorCommand to remove model

field and model-specific timeout fallback.

Added @JsonIgnoreProperties to Configuration for forward compatibility

with old config files that still contain a models key.