Add 3D grid support and end-to-end visualization (training + Plotly)

[HaileyStorm]

Summary

• Adds full 3D grid support across config, world seeding, model/competition, and training.
• Builds on the prior --live-viz work (PR add live training plots flag - --live-viz #1) by extending it to 3D.

Changes

• 3D tensors throughout the core loop: grid_size now (D, H, W) with 2D promotion; seeding/pooling and competition logic updated to 3D; update model uses 3D convolutions.
• Training + W&B: CLI accepts 3D grid sizes; live 3D slice-stack visualization; W&B snapshots/videos use 3D slice montages.
• Visualization tooling: 3D territory volumes, slice-stack renderers (matplotlib/Plotly), population/entropy/compression metrics; Plotly dependency added.
• visualize_trained.py: new viewer for trained runs with 2D/3D live playback and optional Plotly web view.
• Config/docs: example config updated for 3D defaults and viz parameters; README adds 3D examples and viz flags.

Sample 3D commands

• uv run python src/train.py --n-ncas 3 --epochs 200 --grid-size 10 10 10 --live-viz --viz-slice-axis depth
• uv run python src/visualize_trained.py --model-path <run_dir> --grid-size 10 10 10 --plotly