PHILOSOPHY/ARCHITECTURE/agent rules/HIGH_LEVEL_API describe the C -> $
scheme; docs/API.md moves to docs/internal/NATIVE.md (internal, excluded
from release AGENTS.md); docs gate plugin and links updated. $ gains what
games used to take from engine.*: .angularVelocity(), .mass(),
.allowSleep(), $.sound.channel(ch), $.debug.render(). The method-name list
in _CONTRACT.md is regenerated from the live engine (345 names).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>