feat(gui): Grid World Agent Navigation Visualization

[fderuiter]

This PR implements the requested "Grid World" Reinforcement Learning visualizer for the Math Explorer GUI.

Architectural Impact

• Added grid_world.rs extending the existing AiTool strategy interface to seamlessly plug into the AiTab without needing structural refactoring of app.rs.

Feature Summary

• Custom grid state (GridState) and action (Move) structures mapped to the backend State and Action traits.
• Q-Learning implementation directly delegating algorithmic computation to math_explorer backend QLearningAgent and TabularQFunction.
• Custom egui painting rendering the agent, obstacles, goals, and best-action direction arrows.
• Added parameter sliders (Learning rate, Discount factor, Epsilon) for real-time model hyperparameter exploration.

Testing/Verification

• Confirmed successful local build (cargo check)
• Unit tests for the workspace passed locally without regression.
• No raw unwrap() or UI panics introduced.

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PR created automatically by Jules for task 13492445251620749712 started by @fderuiter

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