Revamp Flask GUI layout with project state

[lpurdy01]

Summary

• restructure the Flask templates into a top navigation bar, workflow sidebar, and staged panels for preview, setup, progress, and results
• persist scenario uploads as reusable projects with reset/export routes while tightening field-map detection and SSE visual updates
• expand the GUI documentation, agent guidance, and pytest coverage for project reuse, downloads, and layout behaviour

Testing

• pytest tests/test_gui_flask.py

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https://chatgpt.com/codex/tasks/task_e_68f87495d1c08331a54aefc27808404f

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Resolve field-map outputs relative to solver working dir

When processing field-map events, the path from the log is rewritten relative to the uploaded scenario (output_path = scenario_path.parent / output_path). motor_sim interprets relative output paths relative to its current working directory (the repo root when launched via ./build/motor_sim), so logs such as outputs/domain_field.csv will actually be written under ./outputs, not beside the uploaded JSON. Because the GUI looks in the scenario directory instead, it never finds the CSV, so live previews and the final field-map download remain empty unless a scenario uses absolute paths. _collect_field_outputs applies the same assumption, compounding the problem after the run completes. Consider resolving relative paths against the process CWD (or using Path.cwd()), so default scenarios with relative outputs are discovered correctly.

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