Doc cleanup: Environment is Generic[ActT, ObsT, StateT], not single-param — match real openenv-core API surface

Fix OpenEnv package: swap squatter openenv for openenv-core>=0.2.1, update PROJECT.md API sections and rubrics imports to match real Meta-PyTorch framework

PROJECT.md amendments: turn-budget timer (replaces wall-clock), Section 14.8 reward-hacking defenses, Section 2.5 critical risks for Claude Code awareness

Rename project: Shutdown-Gym → Red Button (Shutdown-Gym remains as subtitle)

Phase 1: Initial scaffold, Claude Code workspace, repo structure per PROJECT.md Section 5