Add Emerald support and PyGBA raw-state save/load

[OrekiDawson]

Summary

This PR adds Pokémon Emerald/GBA support to pokemon-agent by introducing an Emerald memory reader, wiring Emerald detection/selection through the CLI and server paths, and fixing PyGBAEmulator state persistence to use mGBA raw-state APIs.

The save/load behavior now supports raw states generated by pokemon-agent's PyGBA/mGBA backend.

Validation

• uv run pytest test_emerald.py test_imports.py
  • 6 passed
• uv run ruff check pokemon_agent/memory/emerald.py pokemon_agent/emulator.py test_emerald.py
  • passed
• Real Emerald ROM raw-state roundtrip:
  • state_size: 397312 bytes
  • same_after_reload: true
• HTTP acceptance:
  • /health OK
  • /save OK
  • /action wait_60 OK
  • /load OK
  • /load returned Pokemon Emerald (USA)

Known Limitations

External mGBA .ss savestates are intentionally out of scope. Existing .ss files may depend on a different frontend, BIOS, game version, or state serialization format and are not expected to load through this backend.

[OrekiDawson]

Small note on the second commit: the full Gen 1-3 species name table is used by the Emerald memory reader so decoded party/species output is readable across the Emerald Pokédex range. It does not expand the PR scope beyond Emerald/GBA support.

[OrekiDawson]

Follow-up hygiene check against pokeemerald internal constants found one mismatch: Emerald HM item ids are 339-346, not the earlier 259-266 values. Added a small commit fixing those item ids and a regression test; pytest is now 6 passed and ruff remains clean.