Add legend positioning to graph and LeNet views

[mgalore]

Summary

• add the existing six-value legend_position API to graph and LeNet static and animated views
• share legend validation and canvas placement with the flow view so all three styles stay consistent
• expose the option through render(), animation, and the MCP capabilities manifest
• add graph and LeNet gallery examples plus regression coverage for defaults, invalid values, placement, and forwarding

Verification

• PATH="$PWD/.venv/bin:$PATH" .venv/bin/pytest -q — 311 passed
• .venv/bin/pre-commit run --all-files — all hooks passed
• MPLBACKEND=Agg .venv/bin/python docs/examples/graph/plot_legend_position_graph.py
• MPLBACKEND=Agg .venv/bin/python docs/examples/lenet_style/plot_legend_position_lenet_style.py
• git diff --check

Closes #185

[Tariolle]

Looks clean to me