add the Kinematic Explorer

[zeerekahmad]

PR: add the Kinematic Explorer

• branch: zeerekahmad/kinematic-explorer
• base: zeerekahmad/kinematics-wheel-packaging
• commit: f8f0ec0

Description

A Streamlit app for visualising trajectory lattices, kinematic relationships and vehicle footprints across all
three models. Every trajectory it draws comes from the C++ projectors, so the explorer and production code
share one forward-simulation path rather than drifting apart.

• The polymath_kinematics.explorer subpackage holds pure functions — simulation, plotting, export, config
  and types — so they are testable without a Streamlit runtime.
• The app body stays in kinematic_explorer_app.py because that module is the Streamlit script: importing
  it from the console-script entry point would run every widget in bare mode before the server starts, so
  cli.py shells out to streamlit run instead.
• Offers geometry sliders including body overhangs, a front/rear axle reference selector, single-trajectory
  ramp controls, and CSV / JSON / PNG / SVG / PDF download.
• CI widens the wheel job to run the explorer suite, check that the subpackage imports cleanly, and start the
  console script headless — a healthy start is what proves the entry point does not execute the app body on
  import.

Migration Guide

N/A — additive. The Streamlit dependency is confined to the optional [explorer] extra.

Related issues

Completeness checklist

• Is there test coverage? If it was a bugfix, is there a regression test?
• Is user-facing API/behavior documented?
• Is core documentation updated?
• Are all checks green?
• Assign reviewers to the PR and post in #code_reviews

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