feat(gamestate): expose last_tarot_planet for The Fool

[BGarber42]

Summary

• Expose optional last_tarot_planet on GameState from G.GAME.last_tarot_planet (card key The Fool would create, e.g. c_hermit).
• Omitted when no Tarot/Planet has been used yet this run.
• Document in OpenRPC, docs/api.md, and Lua types; add integration tests.

Test plan

• uv run pytest tests/lua/endpoints/test_gamestate.py::TestGamestateTopLevel::test_last_tarot_planet_absent_at_run_start -v
• uv run pytest tests/lua/endpoints/test_gamestate.py::TestGamestateTopLevel::test_last_tarot_planet_after_using_tarot -v
• uv run pytest tests/lua/endpoints/test_gamestate.py::TestGamestateTopLevel::test_last_tarot_planet_after_using_planet -v
• Manually: start a run, gamestate has no last_tarot_planet; use Hermit; gamestate shows last_tarot_planet: c_hermit`

[S1M0N38]

close in favor of

• a7c9b10
• e8233e1

Thanks for this PR. I credited you as co-author. These changes will land in balatrobot v2.