♻️ Replace CLI-based app logs with native WebSocket SDK

[renardeinside]

Summary

• Replace CLI-based databricks apps logs invocation with native WebSocket streaming via databricks_sdk for lower latency and structured output
• Harden SDK types: ComputeState enum with #[serde(other)] for forward compat, Validation error variant, url::Url-based URL helpers, idle timeout for early stream termination, debug logging for deser errors
• Improve MCP handler: ResolvedAppName struct (replaces &mut bool), per-profile DatabricksClient cache (RwLock with double-check), u32 tail_lines, restore from_serializable structured MCP content pattern

Test plan

• 9 new API-level deserialization/validation tests in apx-databricks-sdk (all pass)
• All 32 SDK tests pass (cargo test -p apx-databricks-sdk)
• All 30 MCP lib tests pass (cargo test -p apx-mcp --lib)
• Zero clippy warnings across workspace
• cargo fmt clean

🤖 Generated with Claude Code