v1.3.4

Improved

• AllModelsExhaustedError Messages - Error message now lists each model's error class and message on separate lines instead of only showing the last error. Includes an errors accessor returning structured error data (model, error_class, error_message, error_backtrace).
• Error Backtrace Capture - AttemptTracker now captures the first 20 lines of each error's backtrace, persisted in the execution's attempts JSON column.
• Execution Dashboard Error Display - Error column in the attempts table now shows the error class and message visibly (not hidden in a tooltip). Click "Stack trace" to expand the full backtrace inline. Copy buttons for individual traces and all errors.