[Backend Registry] T02: Implement Enums & Model Struct

[leocamello]

Overview

Define BackendType, BackendStatus, DiscoverySource, and Model with serialization.

Estimated Time: 1.5 hours
Dependencies: #1 (T01)

Tests to Write First

#[test] fn test_backend_type_serialization()
#[test] fn test_backend_status_serialization()
#[test] fn test_discovery_source_serialization()
#[test] fn test_model_creation()
#[test] fn test_model_json_roundtrip()

Implementation Steps

1. Write the 5 tests (they will fail - no impl yet)
2. Implement enums with #[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
3. Use #[serde(rename_all = "lowercase")] for enum variants
4. Implement Model struct with all fields from spec
5. Run tests until all pass

Acceptance Criteria

• All 5 tests pass
• Enums serialize to lowercase strings
• Model has all fields: id, name, context_length, supports_vision, supports_tools, supports_json_mode, max_output_tokens
• cargo clippy passes

References

• Spec
• Plan

[leocamello]

✅ Completed as part of Backend Registry implementation. All tests passing.