Implement CI, tests, and update documentation

[KnightKotOR]

Linter:

• Added Ruff for formatting and linting

Tests:

• Data: Validate data columns and classes balance
• Smoke: Validate imports and inspect signature
• Metrics: Validate F1-macro threshold above 0.85 and no High → Low predictions
• Optuna objective: Validate creation, optimizing study and raise on unknown model
• Invariants: Validate labels (0,1,2); Validate High priority tickets from test either skip if none; Validate that prediction is deterministic

CI:

• On push and pull request into main testing lint and pytests

Docs:

• Updated readme and added pictures for confusion matrix and shap result

Refactoring:

• Added assets folder for readme pictures