Handle gravity-aware monster spawns

[themuffinator]

Summary

• improve gravity-aware spawn validation by normalizing gravity vectors and adjusting drop/clearance traces
• align ground-support checks with arbitrary gravity axes for safe monster placement
• add coverage for standard, inverted, and custom gravity spawn scenarios

Testing

• python tools/ci/run_tests.py (fails: multiple existing test targets do not compile under available standard library; see artifacts/test-results/test-log.txt for details)

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Align spawn helper signatures with declarations

CheckSpawnPoint now requires a gravity vector here, but g_local.hpp and existing callers still declare/use the legacy three-parameter version (e.g., g_local.hpp:4577, m_medic.cpp:1046, m_carrier.cpp:314). The old symbol is therefore left undefined at link time and the new overload is never reached, so the game DLL will not build until the header and call sites are updated (the same mismatch exists for the patched FindSpawnPoint/CheckGroundSpawnPoint signatures).

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